**Did the COVID-19 Lockdown-Induced Hydrological Residence Time Intensify the Primary Productivity in Lakes? Observational Results Based on Satellite Remote Sensing**

**Ram Avtar 1,\*, Pankaj Kumar 2, Hitesh Supe 1, Dou Jie 3, Netranada Sahu 4,5, Binaya Kumar Mishra <sup>6</sup> and Ali P. Yunus 7,8**


Received: 6 August 2020; Accepted: 10 September 2020; Published: 15 September 2020

**Abstract:** The novel coronavirus pandemic (COVID-19) has brought countries around the world to a standstill in the early part of 2020. Several nations and territories around the world insisted their population stay indoors for practicing social distance in order to avoid infecting the disease. Consequently, industrial activities, businesses, and all modes of traveling have halted. On the other hand, the pollution level decreased 'temporarily' in our living environment. As fewer pollutants are supplied in to the hydrosphere, and human recreational activities are stopped completely during the lockdown period, we hypothesize that the hydrological residence time (HRT) has increased in the semi-enclosed or closed lake bodies, which can in turn increase the primary productivity. To validate our hypothesis, and to understand the effect of lockdown on primary productivity in aquatic systems, we quantitatively estimated the chlorophyll-a (Chl-a) concentrations in different lake bodies using established Chl-a retrieval algorithm. The Chl-a monitored using Landsat-8 and Sentinel-2 sensor in the lake bodies of Wuhan, China, showed an elevated concentration of Chl-a. In contrast, no significant changes in Chl-a are observed for Vembanad Lake in India. Further analysis of different geo-environments is necessary to validate the hypothesis.

**Keywords:** hydrological residence time (HRT); lake; COVID; waterbodies

#### **1. Introduction**

The residence time is a fundamental descriptor in hydrology that provides information on the timescales of a molecule of water spend in a specific system. Hydrological residence time (HRT) is estimated as the amount of time the water spent in any section of the connected network [1]. The longer a parcel of water remains in a specific system (river, lake, ponds, etc.), the longer is its

residence time, and vice versa. HRT has got important applications in a wide range of hydrological fields including water quality analysis, stratification, habitat ecology, age dating, water mixing and circulation, microbiological contaminants, etc., [2–4]. For example, Zwart et al. [4] showed that lakes with short HRT had higher dissolved organic carbon and greater net heterotrophy. Hein et al. [5] and others noticed that a prolonged residence time increases the primary productivity in aquatic systems. Similar observations have been noticed in several other works. For instance, León et al. [6] reported that chlorophyll-*a* was directly related to the HRT. Stumpner et al. [7] showed that zones of longer HRT (15–60 days) have higher Chl-*a* concentrations, and ones of shorter HRT (1–14 days) have lower Chl-a concentrations.

The SARS-CoV-2, or popularly the Coronavirus Disease 2019 (COVID-19) that affected the world population in early 2020, caused several nations and territories to a stand-still. Over 25 million infected persons and more than 860,000 deaths have been reported worldwide caused by the COVID-19 as of 1 September 2020 [8]. Since no vaccine or cure has developed to protect the body against the COVID-19, complete or partial lockdown has been induced in many countries and territories to stop the chain of infection. As vehicular movement halts, construction is put on hold, and industries stop production, the levels of pollution level has come down both in atmosphere and hydrosphere [9,10].

The industrial sewage input to the lakes through inlets, recreational activities in lakes such as boating, fishing, etc., stopped temporarily in aquatic systems during COVID-19-induced lockdown. We hypothesize that the hydrological residence time in closed or semi-enclosed lakes has increased, which may, in turn, increase the primary productivity. To validate our hypothesis and to understand the effect of lockdown on primary productivity in aquatic systems, this study explores to quantify the level of Chl-*a* before and during the lockdown period using remote sensing techniques. Chl-*a* derived from OC3 algorithm [11] is selected for comparing the eutrophication status before and during the lockdown.

While, the hydrological residence time is not the only factor that influence the primary productivity, other factors such as temperature, increased light exposure, oxygen level, initial nutrients levels, etc., also could cause an increase or decrease in the level of Chl-*a* concentration in the aquatic environments [12–14]. For instance, Castelao et al. [15] using geostationary satellite data showed the seasonal development of coastal upwelling in which the maximum was peaked in the summer and minimum during the winter. In oligotrophic waters, maximum phytoplankton production often occurs near the top of a nutricline [16]. In addition, in inland water bodies the intensity of monsoon rainfall and landscape heterogeneity tremendously influenced the Chl-*a* concentrations [17]. Further, in places of upwelling areas, the water surface temperatures are often cooler than nearby waters, resulting in an increased chlorophyll concentration. However, we assume in this study that the boundary conditions remain unchanged during the observation period for both the study areas and, hence, examined the effect of HRT on water quality.

#### **2. Study Area**

The stringent and biggest of all lockdown was imposed in two places, (i) Wuhan, China, the epicenter of COVID-19, and (ii) India, where 1.3 billion people have been staying home since 25 March 2020. Hence, we selected some lake bodies in Wuhan city (Figure 1a) and one lake body in India (Vembanad Lake, the longest freshwater lake in India) (Figure 1b). These lake bodies are also preferred because of the availability of cloud-free remote sensing images, and expected longer HRT caused by the stringent lockdown in these areas. Both the selected cases experienced severe pollution by wastewater disposal, industrial effluents, heavy metal concentration, and micro-plastics before the lockdown [18,19].

**Figure 1.** Location of the study area (**a**) lakes of Wuhan, China, and (**b**) Vembanad Lake, India.

#### **3. Data and Methodology**

#### *3.1. Theoretical Framework*

The amount of water spent in any section of the water body is an important consideration for many water quality problems [1]. In general, the regions near the inlet are having less residence time than the far places. Further, in a closed water body or semi-closed lakes, the movement of water is largely constrained, therefore having longer residence time. Dickman, [20] showed that increased water residence time more likely increases the algae bloom, especially for small reservoirs. Several other works showed that Chl-*a* increases with increasing residence time and decreases with increasing discharge [21,22]. The hydrological residence time in our study area was expected to increase during the lockdown period owing to following reasons: (i) sewage disposal to the lakes has completely stopped, causing reduced discharge via inlets, and (ii) all anthropogenic activities, including boating has stopped during the lockdown period, causing still waters. The lockdown induced by COVID-19 in this ecosystem with a long retention time, thus offering an opportunity to study the development of phytoplankton that are otherwise adapted to a turbid environment.

While HRT has been traditionally measured through dye-tracer experiments in the field or estimating the ratio of the volume of the domain of interest to an outgoing flux [23]. Recently, physically based hydrodynamic modeling is employed to estimate the residence [24]. In this study, we assumed that the HRT is the longest during the lockdown period.

#### *3.2. Image Acquisition and Data Processing*

Landsat 8 OLI images and Sentinel-2 images of the immediate pre-lockdown period (December 2019 and January 2020) and during the lockdown period (February–April 2020) were downloaded (Table 1) from the United States Geological Survey (USGS) website (earthexplorer.usgs.gov). All scenes had undergone terrain correction within prescribed tolerances. Table 1 shows the details of satellite images used in this study for Chl-*a* mapping. The Level 1 Landsat-8 and Sentinel-2 images were further treated using ACOLITE software for radiometric calibration (Top of Atmosphere Reflectance) and atmospheric correction (Surface Reflectance). ACOLITE, developed by Royal Belgian Institute of Natural Science, employs a "dark spectrum fitting" (DSF) approach [25,26] for atmospheric correction. For detailed procedure on atmospheric correction for Landsat-8 OLI in an ACOLITE environment, readers are referred to the following references [27,28]. For validation purpose, we used the satellite images of 2017–2019 March–April images. The validation dataset was directly used in Google Earth Engine (GEE) platform with the help of chlorophyll index algorithm [14]. The GEE codes are provided in the Supplementary File S1.

The variability in the meteorological conditions during the study period may affect the chlorophyll concentrations. While the regional air temperatures were increasing from December to April by about 10◦ Celsius for Wuhan, the average temperature difference was only about 2◦ Celsius for Vembanad region (source: https://www.timeanddate.com). The precipitation condition was normal for both case areas with occasional rainy days observed during the study period (Figure 2).

**Figure 2.** Daily precipitation (mm) time series chart for (**a**) Wuhan and (**b**) Vembanad (Cochin) during the study period (source: CHIRPS Daily: Climate Hazards Group InfraRed Precipitation with Station Data (version 2.0)).


**Table 1.** Details of the satellite images used for mapping chlorophyll-*a* (Chl-*a*) before and during the lockdown period in 2020.

#### *3.3. Chlorophyll-a Retrieval*

The reflectance ratio of blue and green wavelengths in the electromagnetic spectrum was recognized to correlate well with the distribution of chlorophyll in surface waters [29–31]. Several studies have supported the usage of blue-green bands on the assumption that any changes in these wavelengths are driven by changes in phytoplankton concentrations [32,33]. The performance of blue-green ratioed algorithms for retrieving Chl-*a* was tested independently in different environments [34–38]. We, therefore, employed the OC3 algorithm [11], which uses the water leaving reflectance (Rrs) in wavelength 443, 482, and 561 for Landsat 8 (Equations (1)–(4)), and 490 and 560 for Sentinel 2 sensor (Equations (1)–(3), and (5)). Mathematically, OC3 Chl-*a* algorithm is expressed as:

$$\text{Cll}\_{\text{OC}3} = 10^y \tag{1}$$

$$y = a\_0 + a\_1 \mathbf{x} + a\_2 \mathbf{x}^2 + a\_3 \mathbf{x}^3 + a\_4 \mathbf{x}^4 \tag{2}$$

$$\mathbf{x} = \log\_{10}(\mathbf{R}) \tag{3}$$

$$R = \frac{\max\left(R\_{\mathbb{R}^3}(443, 482)\right)}{R\_{\mathbb{R}^3}561} \tag{4}$$

$$R = \frac{R\_{rs}490}{R\_{rs}560} \tag{5}$$

The coefficients 0.2412, −2.0546, 1.1776, −0.5538, −0.4570 are, respectively, used for *a*<sup>0</sup> to *a*<sup>4</sup> (https://oceancolor.gsfc.nasa.gov/atbd/chlor\_a/). The performance evaluation of Chl-*a* retrievals using Sentinel-2 data and OCx algorithms based on Acolite was found within the root mean squared logarithmic error (RMSLE) of 1.2–1.3 [39]. In another study, by employing OC3 algorithm for Indonesian seas, the RMSE of in situ vs. satellite Chl-*a* was found within the range of 0.04–0.05 [40], suggesting superior performance of satellite retrievals of Chl-*a* in aquatic systems.

#### **4. Results and Discussion**

#### *4.1. Lakes in Wuhan*

Figures 3 and 4a presents the Chl-*a* concentration maps of lakes in Wuhan for pre-lockdown (7 December 2019; 20 January 2020), during the lockdown (30 January 2020; 9 February 2020; 15 and 20 March 2020) and post-lockdown periods (9, 13 and 29 April 2020). It can be seen that the mean Chl-*a* concentrations were very low in the pre-lockdown period (2.77 and 2.95 μg/L) and immediately after the lockdown period (2.25 μg/L). By 9 February, the mean concentration gradually increased to 3.05 μg/L. Note that the lockdown was imposed on 23 January in Wuhan. The peak Chl-*a* was observed in the March months (6.57 and 5.88 μg/L), which also corresponds to the peak period of the quarantine period in Wuhan. The lockdown ended on April 8; the mean Chl-*a* for April shows a gradually decreasing trend (5.06, 4.49, and 4.74 μg/L).

**Figure 3.** Chlorophyll-*a* concentration before, during, and post the lockdown period estimated using OC3 algorithm for Wuhan scenic lakes.

**Figure 4.** Mean chlorophyll-*a* during pre, during, and post lockdown in (**a**) Wuhan Lake and (**b**) Vembanad Lake (error bar shows ± standard deviations).

#### *4.2. Vembanad Lake, India*

Figures 4b and 5 present the results of Chl-*a* concentration before (28 February 2020; 15 March 2020; 24 March 2020) and during the lockdown period (31 March 2020; 4 April 2013; 13 April 2013; 16 April 2020). Note that the lockdown started on 25 February in India and was still ongoing during the study period. Contrary to the former analyzed area, Lake Vembanad does not show any significant increase in primary productivity during the lockdown period. Nevertheless, the concentration was not decreased during this period (Figure 4b).

**Figure 5.** Chlorophyll-*a* concentrations before and during the lockdown period estimated using OC3 algorithm for Vembanad Lake waters.

#### *4.3. Validation*

Since there is an ~10◦ celcius increase in temperature from December to April in Wuhan climatology, it is expected that the Chl-*a* also increased during this time period. In order to validate the hypothesis that the increased Chl-*a* in the lakes of Wuhan during the lockdown period in 2020 is because of the increased HRT, we monitored the Chl-a for the previous years (2017, 2018, and 2019) during the same time period. The comparative maps of mean Chl-*a* for 2020 (March–April) and those of previous years (2017–2019) during the same time period are presented in Figure 6. It can be seen that the Chl-*a* during 2020 March–April is the maximum among the study years, especially in the lakes far away from the city center. This implies that hydrological residence time was maximum in places where the influence of human activity was minimum and, indeed, strengthen our results presented in Section 4.1.

**Figure 6.** Mean chlorophyll-*a* concertation mapped for (**a**) 2017, (**b**) 2018, (**c**) 2019, and (**d**) 2020 during April–May months (for simplicity, the chlorophyll index algorithm [14] is used in Google Earth Engine (GEE) to derive the low to high classes).

#### **5. Discussion and Concluding Remarks**

As the pollutant discharges into lakes and human activities (boating and fishing) stopped or reduced during the COVID-19 lockdown period, we investigated whether the residence time in lakes also increased in associated with it? We tried to answer the problem mentioned above by analyzing the primary productivity in the lakes. Reynolds, [41], and others reported that increased residence time favors Chl-*a* and biomass accumulation in aquatic systems [7]. In our study, we noticed an elevated level of Chl-*a* for the lakes of Wuhan during the initial phase of the lockdown period, followed by a decreasing trend (Figure 4a). This elevated Chl-*a* indicates an increased HRT in the lakes of Wuhan. The decreasing trend followed by the increase may be because a prolonged HRT can settle down the surface phytoplankton [42].

On the other hand, the Vembanad Lake in India does not show any significant changes in Chl-*a* concentration during the lockdown period. A possible explanation is that the Vembanad Lake is not a closed lake, unlike the lakes in Wuhan. Seven rivers are draining into it, plus it has an opening to the Arabian Sea in the north-west, which carries salt water up to 26 km inside the lake during the high-tide period. Thus, it may be because the discharge from the rivers (without pollutants) and tidal action cause the HRT to be insufficient for enhancing primary productivity in the Vembanad Lake. It is noteworthy to mention here that both cases, i.e., Wuhan lakes and the Vembanad Lake, have shown a significant decrease in suspended particulate matter during the lockdown period [10] (Supplementary Materials Figures S1 and S2).

One may, though, argue that the increased Chl-*a* in Wuhan lakes can also be associated with increased water temperature. However, time series Chl-*a* maps compared for different years (2017–2020) show that the year 2020 experienced the maximum value of chlorophyll in the lakes of Wuhan. This demonstrates that Chl-*a* concentration during the lockdown has increased in a closed lake system, i.e., for Wuhan, whereas the Chl-*a* remains unchanged in an open lake system such as the one demonstrated for Vembanad Lake in India. The hydrological residence time induced during the lockdown is by large the influencing factor on increased Chl-*a*, in that it can describe the prolonged residence time increases the primary productivity in closed systems.

The Chl-*a* retrieval using NASA's OC3 algorithm, however, was not validated in this study with spatiotemporally matched field-derived measurements of chlorophyll because of stringent lockdown measures in both cities. However, the capability of OC3 for Chl-*a* retrieval in inland lakes and ocean waters in previous studies show a near one-to-one relationship and can be accounted for the Chl-*a* variability up to upper 10 m of the water column [43]. In addition, the research framework also does not incorporate the variability of Chl-*a* caused by other natural phenomena's, and the amount of water contaminant flow into lakes from household wastes, which are usually difficult to model in satellite-based bio-physical parameter estimations. Nevertheless, the methodology and results presented in our study can help in understanding the influence of lockdown on water quality parameters, especially phytoplankton concentrations. Thus, although the research framework can offer important insights into short-term changes in the hydrosphere, additional analysis incorporating time-series data, and similar studies in closed lakes in other climatic environments is necessary to further validate our hypothesis.

**Supplementary Materials:** The following are available onlsupine at http://www.mdpi.com/2073-4441/12/9/2573/s1, Figure S1: Decreased suspended particulate matter in different lakes of Wuhan during the lockdown period, Figure S2: Decreased suspended particulate matter in Vembanad lake during the lockdown period, Text S1: Codes for chlorophyll index using Sentinel-2 images in GEE.

**Author Contributions:** Conceptualization: R.A., A.P.Y.; methodology: R.A., A.P.Y.; validation: R.A., A.P.Y.; writing—original draft: R.A., P.K., H.S., D.J., N.S., B.K.M., A.P.Y.; writing—review and editing: R.A., P.K., H.S., D.J., N.S., B.K.M., A.P.Y.; funding acquisition, R.A., A.P.Y. All authors have read and agree to the published version of the manuscript.

**Funding:** This research received no external funding.

**Acknowledgments:** Authors would like to thank Hokkaido University L-station and SOUSEI support for Young Researcher. Furthermore, the authors are thankful to the United States Geological Survey (USGS) and Copericus hub for providing satellite data and ACOLITE software provided by RBINS. We also acknowledge the support of Dr. Masago Yoshifumi and appreciate the contribution made by the anonymous reviewers.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

## *Communication* **Exposure to SARS-CoV-2 in Aerosolized Wastewater: Toilet Flushing, Wastewater Treatment, and Sprinkler Irrigation**

**Muhammad Usman 1,\*, Muhammad Farooq 2, Muhammad Farooq <sup>3</sup> and Ioannis Anastopoulos 4,\***


**Abstract:** The existence of SARS-CoV-2, the etiologic agent of coronavirus disease 2019 (COVID-19), in wastewater raises the opportunity of tracking wastewater for epidemiological monitoring of this disease. However, the existence of this virus in wastewater has raised health concerns regarding the fecal–oral transmission of COVID-19. This short review is intended to highlight the potential implications of aerosolized wastewater in transmitting this virus. As aerosolized SARS-CoV-2 could offer a more direct respiratory pathway for human exposure, the transmission of this virus remains a significant possibility in the prominent wastewater-associated bioaerosols formed during toilet flushing, wastewater treatment, and sprinkler irrigation. Implementing wastewater disinfection, exercising precautions, and raising public awareness would be essential. Additional research is needed to evaluate the survival, fate, and dissemination of SARS-CoV-2 in wastewater and the environment and rapid characterization of aerosols and their risk assessment.

**Keywords:** SARS-CoV-2; COVID-19; bioaerosol; aerosolized wastewater; environmental transmission; agriculture

#### **1. Introduction**

Recent research has demonstrated that people with coronavirus disease 2019 (COVID-19), even those who do not develop symptoms, discharge its etiologic virus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), through their excrement [1]. The presence of SARS-CoV-2 RNA in sewage raises the possibility of analyzing wastewater for the epidemiological monitoring of COVID-19 [2]. Therefore, researchers in many countries are tracking SARS-CoV-2 in wastewater as a complementary approach to monitor the spread of COVID-19 [1].

The widespread existence of SARS-CoV-2 throughout wastewater systems could have important implications in the environmental transmission of COVID-19 [2–4]. Potential health concerns due to direct waterborne exposure to this virus in wastewater are well documented [5–7]. However, the aerosolized pathway must also be considered in this context as it could offer a more direct respiratory pathway for human exposure to SARS-CoV-2. Aerosolized viruses are often produced locally in buildings and on a larger scale during wastewater treatment or irrigation [8,9]. This short review is intended to highlight the potential implications of aerosolized SARS-CoV-2 generated from the top three wastewaterassociated sources of aerosol: toilet flushing, wastewater treatment, and sprinkler irrigation. Consistent with WHO, and the literature, here the term aerosol is referred for the small breathable particles of <10 μm (PM10) that can remain airborne with the capability of shortand long-range transport [10].

**Citation:** Usman, M.; Farooq, M.; Farooq, M.; Anastopoulos, I. Exposure to SARS-CoV-2 in Aerosolized Wastewater: Toilet Flushing, Wastewater Treatment, and Sprinkler Irrigation. *Water* **2021**, *13*, 436. https://doi.org/10.3390/ w13040436

Academic Editor: Pankaj Kumar Received: 25 December 2020 Accepted: 5 February 2021 Published: 8 February 2021

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

Inhalation of respiratory droplets/aerosols and/or interactions with contaminated surfaces are the main transmission routes of SARS-CoV-2, which is a highly contagious virus [11]. According to WHO (2020), airborne transmission of this virus is possible during aerosol-generating medical events. However, as reported in its scientific brief of 9 July, 2020, WHO is also evaluating the possibility of SARS-CoV-2 spread through aerosols in the absence of aerosol-producing processes [11]. Experimental studies involving aerosols of infectious samples found that SARS-CoV-2 can remain viable for up to several hours [12,13]. Moreover, aerosols are likely to contribute to longer-range transport and potential infection from the pathogens [10]. Therefore, it is critical to assess the potential of the aerosolized pathway where the probability of direct respiratory exposure to SARS-CoV-2 is substantially higher. In this context, SARS-CoV-2 in aerosolized wastewater becomes an important scenario in its exposure pathways that should not be ruled out.

#### **2. Exposure to SARS-CoV-2 in Aerosolized Wastewater**

Although there is currently no proof of wastewater-related exposure to SARS-CoV-2, the contribution of aerosolized wastewater as a transmission route was recognized during the SARS epidemic of 2003 [14]. Respiration of virus-laden aerosols, created through the defective plumbing and sewage system, was recognized as a potential transmission route within a housing complex in Hong Kong where 187 people were infected [14]. Therefore, the transmission of this virus in aerosolized wastewater remains a significant possibility in the following scenarios: toilet flushing, wastewater treatment, and sprinkler irrigation (Figure 1). These scenarios are briefly described in the following sections.

**Figure 1.** Overview of potential dissemination of SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) via aerosolized wastewater.

#### *2.1. Bioaerosol Generation by Toilet Flushing*

The toilet flushing creates a great deal of turbulence that generates bioaerosols containing pathogenic microorganisms [8]. For example, Wilson et al. [15] reported that toilet flushing increased the concentration of pathogens such as *Clostridioides difficile* in hospital air. Moreover, 95% of these droplets were small enough (<2 μm diameter and >99% <5 μm) to present an airborne infection concern [16,17]. A full-scale pilot experiment on a two-story wastewater plumbing system using *Pseudomonas putida* (as a model pathogen

being flushed into the system) revealed that pathogens can be aerosolized and transmitted between rooms [18]. Droplet fallout contaminated the surfaces within the system and rooms. Recently, Li et al. [19] used computational fluid dynamics to model fluid flows to estimate how far aerosol particles may transport due to toilet flushing. The simulations show a substantial upward transport of virus particles, 40–60% of which rise above the toilet seat and may reach to a height of 106.5 cm from the ground. Moreover, these particles remain suspended in the air more than a minute after the flush [19]. An analysis in two hospitals from Wuhan, China revealed that the concentration of SARS-CoV-2 RNA was high in patient toilets, while it was very low in aerosols in ventilated patient rooms and isolation wards [20]. In a hospital for COVID-19 patients, Ding et al. [21] marked toilets as the high-risk area where most of the identified SARS-CoV-2 RNA in the hospital emerged from the fecal-derived aerosols. Thus, bioaerosols generated by toilet flushing could potentially contribute to the environmental transmission of SARS-CoV-2. Though there does not exist any specific research on the toilet-associated generation of infectious bioaerosols containing SARS-CoV-2, it would be judicious to use precautions to prevent this transmission route [9]. Closing the lid on the toilet before flushing and cleaning the toilet seat before using it has been recommended [17,19]. Environmental disinfection of toilet areas should be imposed in healthcare facilities and public toilets [20]. Toilets are generally indoor, having limited potential for aerosolized virus dilution as compared with the outdoor settings (wastewater treatment facilities and sprinkler irrigation systems). It has also been recommended to ensure sufficient and effective ventilation, possibly enhanced by air filtration and disinfection [22]. In addition, modification in toilet designs should also be considered [19]. Raising public awareness is crucial to impede the toilet-associated transmission of SARS-CoV-2.

#### *2.2. Bioaerosol Produced during Wastewater Treatment*

Wastewater contains a high number of pathogens such as viruses, bacteria, and parasites. Processes involved in wastewater treatment may lead to the aerosolization of these pathogens [23,24]. Therefore, bioaerosols generated at cooling towers and wastewater treatment plants (WWTPs) have been widely considered as a potential health hazard for sewage workers and nearby communities [24,25]. For example, Masclaux et al. [23] found adenovirus RNA in 100% of summer air samples of WWTP and 97% of winter samples. They detected norovirus in only 3 of the 123 air samples, but no sample contained the hepatitis E virus. Courault et al. [25] detected hepatitis E virus and norovirus RNA in the aerosol produced from active sludge basins of WWTPs and in that of plots irrigated with the treated water. Indeed, risks of SARS-CoV-2 aerosolization can be particularly high in uncovered aerobic wastewater treatment facilities like an aerobic tank [26] and activated sludge process [23]. The potential for the coronaviruses to become aerosolized increases with the transport in water [27], particularly during the pumping of wastewater, during its discharge and subsequent flow through the drainage network [28]. Substantial load of SARS-CoV-2 arriving at WWTPs should raise concerns for its aerosolization and ultimate implications in public health. Due to the significant concentrations of SARS-CoV-2 RNA in wastewater, WWTPs are gaining attention for early tracking and removal of this virus [29]. The viral loads can be decreased in WWTPs by wastewater disinfection and filtration [3,30]. However, the effects of the disinfection process on the microbial community in wastewater, antimicrobial resistance, and associated environmental risks should also be considered [31]. Safety practices should be particularly ensured to protect the health of sanitation workers.

#### *2.3. Bioaerosol Produced during Irrigation*

The use of sprinkler/spray irrigation is prevalent in many countries to apply treated wastewater in urban green spaces and agricultural soils. Sprinkler irrigation can potentially aerosolize the pathogens if present in the wastewater [32]. It can provide a respiratory route for exposure to the irrigators and community members in the vicinity [25,33]. In addition to the irrigation method, viruses and other pathogens transported to the soil by irrigation water can also be aerosolized later during windy spells [34]. Indeed, 1–15% of viruses transported to the soil with irrigation water were aerosolized, of which 11–89% were aerosolized within the first 30 min [34]. Risk assessment of airborne enteric viruses, released from wastewater used for irrigation in France, revealed that an increase in wind speed and a decrease in distance from the pathogen source can significantly increase the probability of infection [25]. Similarly, pathogens can be aerosolized in wastewater canals [35]. This can pose disproportionate risks to developing communities having poor sewage infrastructure. As reported in the 2017 World Water Development Report of the United Nations, 80% of wastewater worldwide (>95% in some developing countries) is discharged into the environment without suitable treatment.

#### **3. Concluding Remarks and Perspectives**

The COVID-19 patients discharge infectious SARS-CoV-2 virus in their feces [36,37], highlighting the potential of transmission through fecal–oral route. However, the existing data on SARS-CoV-2 detection in wastewater were obtained by PCR and not by cell infection. Therefore, there exists a clear knowledge gap regarding the detection of infectious SARS-CoV-2 in wastewater. Moreover, further research is needed to assess the survival of the infectious viruses in wastewater. The evidence from surrogate corona viruses such as murine hepatitis virus (MHV) and transmissible gastroenteritis virus (TGEV) showed that it takes at least 10 days for 99% inactivation of these viruses in lake water [38]. That may further highlight the transmission potential of corona viruses such as SARS-COV2 through wastewater.

Though there is no concrete evidence for the spread of SARS-CoV-2 through aerosolized wastewater, its role in the environmental transmission of COVID-19 cannot be ruled out. Protection of workers in these fields needs immediate attention. For that, authorities should ensure that workers, particularly those facing greater exposure risk, have access to appropriate protective equipment, adequate training in infection control, high testing rates, and paid sick leave. The situation is particularly critical in developing communities due to poor sewage infrastructures and their lack of access to adequate water and hygiene facilities. Substantial viral load within aerosolized wastewater calls for effective disinfection of wastewater to prevent the formation of pathogen-laden aerosols. Expertise in wastewater science and technology would be required, whereas transition to the aerosol phase calls for treatment according to aerosol standards. Research is also needed for the rapid characterization of aerosols, measurement of SARS-CoV-2 in wastewater aerosols, and their risk assessment.

**Author Contributions:** M.U.: Conceptualization, Writing—Review and Editing, M.F. (1): Writing— Review and Editing, M.F. (2): Writing—Review and Editing, I.A.: Writing—Review and Editing. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by a research grant to M. Usman from Madayn—Public Establishment for Industrial Estates, Oman (CHAIR/DVC/MADAYN/20/02).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** No new data were created or analyzed in this study. Data sharing is not applicable to this article.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


## *Review* **Nexus between Water Security Framework and Public Health: A Comprehensive Scientific Review**

**Sushila Paudel 1, Pankaj Kumar 2,\*, Rajarshi Dasgupta 2, Brian Alan Johnson 2, Ram Avtar 3, Rajib Shaw 4, Binaya Kumar Mishra <sup>5</sup> and Sakiko Kanbara <sup>6</sup>**


**Abstract:** Water scarcity, together with the projected impacts of water stress worldwide, has led to a rapid increase in research on measuring water security. However, water security has been conceptualized under different perspectives, including various aspects and dimensions. Since public health is also an integral part of water security, it is necessary to understand how health has been incorporated as a dimension in the existing water security frameworks. While supply–demand and governance narratives dominated several popular water security frameworks, studies that are specifically designed for public health purposes are generally lacking. This research aims to address this gap, firstly by assessing the multiple thematic dimensions of water security frameworks in scientific disclosure; and secondly by looking into the public health dimensions and evaluating their importance and integration in the existing water security frameworks. For this, a systematic review of the Scopus database was undertaken using Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. A detailed review analysis of 77 relevant papers was performed. The result shows that 11 distinct dimensions have been used to design the existing water security framework. Although public health aspects were mentioned in 51% of the papers, direct health impacts were considered only by 18%, and indirect health impacts or mediators were considered by 33% of the papers. Among direct health impacts, diarrhea is the most prevalent one considered for developing a water security framework. Among different indirect or mediating factors, poor accessibility and availability of water resources in terms of time and distance is a big determinant for causing mental illnesses, such as stress or anxiety, which are being considered when framing water security framework, particularly in developing nations. Water quantity is more of a common issue for both developed and developing countries, water quality and mismanagement of water supply-related infrastructure is the main concern for developing nations, which proved to be the biggest hurdle for achieving water security. It is also necessary to consider how people treat and consume the water available to them. The result of this study sheds light on existing gaps for different water security frameworks and provides policy-relevant guidelines for its betterment. Also, it stressed that a more wide and holistic approach must be considered when framing a water security framework to result in sustainable water management and human well-being.

**Keywords:** water security; water insecurity; water scarcity; water security framework; public health; primary health care; COVID-19

**Citation:** Paudel, S.; Kumar, P.; Dasgupta, R.; Johnson, B.A.; Avtar, R.; Shaw, R.; Mishra, B.K.; Kanbara, S. Nexus between Water Security Framework and Public Health: A Comprehensive Scientific Review. *Water* **2021**, *13*, 1365. https:// doi.org/10.3390/w13101365

Academic Editor: Luís Filipe Sanches Fernandes

Received: 2 April 2021 Accepted: 11 May 2021 Published: 14 May 2021

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

#### **1. Introduction**

Water security is a concept that has recently gained widespread global attention. With the increase in population, rapid urbanization, overexploitation of natural resources, encroachment on natural forests, declining soil fertility, lack of capacity to adapt to climate change, and inadequate capacity of institutions for water management, achieving water security has become one of the emerging global challenges [1–3]. Nearly 1.8 billion people worldwide are already living in countries experiencing high water stress or scarcity [4], and by 2025 more than 2.8 billion people in 48 countries may face water stress [5]. Furthermore, the number of people exposed to water stress could double by 2050, when compared to 2010 [5]. All stakeholders must act quickly to address these challenges of rapid population growth, natural resource degradation, and climate change for better adaptation and achieving water security in a timely manner [3].

Over the last few decades, the concept of security has moved beyond a narrow emphasis on military threats and conflicts to wider concepts of human security, wherein water serves as a central link between health, economic, political, personal, food, energy, and environmental aspects of human security [6]. While the term 'water security' has been conceptualized with a variety of meanings by different scholars, managers, planners, and stakeholders to fit in their specific contexts [7], the United Nations task force on water security has holistically defined water security as "*the capacity of a population to safeguard sustainable access to adequate quantities of acceptable quality water for sustaining livelihoods, human well-being, and socio-economic development, for ensuring protection against water-borne pollution and water-related disasters, and for preserving ecosystems in a climate of peace and political stability*" [4].

Water security is a key factor affecting public health. According to the Sustainable Development Goal (SDG) 6 synthesis study [4], 2.1 billion people lack access to clean drinking water, 4.5 billion people lack access to safely managed sanitation, 0.9 billion people still practice open defecation, and in the least developed nations only 27% of the population has access to soap and water for hand sanitation. In particular, vulnerable groups (e.g., ethnic minorities, children, the urban poor) are those who typically suffer most. Inadequate accessibility to clean water is also often linked with gender inequality. Every day, women and girls are estimated to spend 200 million hours hauling water around the world. In rural Africa, the average woman walks 6 km a day to carry 40 pounds of water [8]. These factors can negatively affect women's opportunities for pursuing education and careers. When there is an absence, insufficient or poorly regulated water and sanitation services, individuals become vulnerable to different preventable health risks [9]. From an environmental point of view, water-related diseases can be waterborne diseases caused by ingestion of contaminated water (e.g., Diarrhea, typhoid); water-washed diseases caused by poor personal hygiene (ex. lice, skin rashes), water-based diseases caused by parasites living in the water (e.g., some helminths), and diseases transmitted by water-associated insect vectors that breed in water (e.g., dengue, malaria) [10].

The incidence of outbreaks depends on the level of scarcity, population density, economic growth, extreme weather events [11]. When people lack even a basic drinking water service, they depend on surface water and/or wastewater that is not safe. Already, at least two billion people around the world are using drinking water sources that are contaminated with feces [9]. Water-borne diseases also occur through leakage of contaminated run-off water, or within the distribution of pipe systems [12].

Despite advancements in science and technology and water security measures, waterborne diseases kill 2195 children every day which is more than AIDS, malaria, and measles combined. This accounts for 1 in 9 child deaths worldwide, making waterborne diseases the second leading cause of death among children under the age of five, even in the 21st century [13]. Diarrheal diseases, the most common type of waterborne diseases, are particularly serious for children and vulnerable people in low-income countries [9]. On top of that, occasional climate-related hazards such as floods and droughts can further increase the pathogen load making water unsafe to drink. Flood can damage water infrastructures, sanitation facilities, reduces water quality, and can mix up drinking water with industrial and agricultural waste, increasing the risk of waterborne diseases [14] while droughts lead to shortages of water and poor water quality [13,15,16].

The risk has been even greater due to the emergence of SARS, MERS, and now COVID-19 [17]. Furthermore, water scarcity, poor quality, and poor accessibility to clean water can lead to additional mental health conditions such as persistent psychological stress, social alienation, intra-community disputes, despair, hopelessness, depression, and anxiety especially in developing countries [18,19]. Finally, due to rapid global changes including climate change, land-use change, and population growth, the risks of waterborne diseases are expected to further increase [2].

There are several frameworks or assessments developed to measure water security with various scales, aspects, and dimensions [7,20–22]. Considering the above-mentioned facts, health-related issues cannot be denied as a focal point or dimension to designing the water security framework. Thus, a comprehensive understanding of how health has been incorporated as a dimension in water security frameworks in different contexts around the world is needed. This research aims to address this need through a systematic analysis of existing water security frameworks, seeking to answer the following research questions:


#### **2. Materials and Methods**

A systematic literature review was conducted, using the Scopus database (http:// www.scopus.com/, accessed on 5 December 2020) to collect existing literature related to water security frameworks. For this analysis, we followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines to document our literature review process [23]. As the search query, we used the Boolean string: TITLE-ABS-KEY (water security) AND (TITLE-ABS-KEY (framework) OR TITLE-ABS-KEY (assessment) OR TITLE-ABS-KEY (health AND hazard)). Publication dates for the search were limited from the year 2000 to 2020, and all searches were limited to the English language texts. The full-texts of all articles retrieved from this search were downloaded and manually screened, and articles meeting any of the following inclusion criteria were used for further analysis: (1) articles discussing water security frameworks or assessments with or without an associated hazard; (2) articles reporting dimensions, components, or indicators of water security; or (3) articles including the term 'health'. Finally, papers matching our inclusion criteria were reviewed and the following information extracted: (a) Spatiotemporal information (i.e., the publication date and location of the studies); (b) the context in which the term water security was used (e.g., in relation to hazard-prone areas, lack of water infrastructure, water pollution, etc.); (c) the key components of the water security framework described in the study; (d) direct and indirect health impacts mentioned, and the importance given to health-related issues in framing a water security framework.

#### **3. Results**

The results of our literature search using the PRISMA guidelines are shown in Figure 1. A total of 933 papers were initially retrieved from Scopus using our defined search query. After a manual screening of these 933 articles, a total of 77 articles were found to be matching our defined inclusion criteria. All other journal articles not matching our inclusion criteria, as well as book chapters, conference papers, and other non-peer reviewed reports were excluded from further analysis.

**Figure 1.** PRISMA flowchart of review results.

#### *3.1. Spatio-Temporal Identity of the Available Literature on Water Security*

As shown in Figure 2, all papers matching our inclusion criteria were published between the years 2008 and 2021. The number of articles published per year showed an increasing trend starting from 2015, with almost 79 percent (61 out of 77) of papers on water security being published since 2015. This suggests increasing global attention toward the issue of water security in recent years, possibly as a result of the SDGs (which were agreed upon in 2015), as one of these global goals (i.e., SDG 6: "Clean water and sanitation for all") is directly linked to water security. Indeed, the SDGs have pushed countries around the world to think more holistically about achieving sustainable water development through attaining water security.

With regards to the geographic focus of the articles, 81 percent (*n* = 62) focused on water security in a particular continent, while the remaining 31 percent (*n* = 24) did not mention any specific region. The spatial distribution of the study locations is plotted on a world map (Figure 3). It is found that the majority of the studies related to water security frameworks and health were focused on the Asian continent (*n* = 29), followed by North America (*n* = 12). Conversely, relatively few studies focused on Africa, Australia, Europe, and South America. In terms of the countries that were the focus of most studies, China was the most common (*n* = 10), followed by Canada (*n* = 6). Only one study (1 of 77) covered Europe. However, this study found 24 papers, which did not have any geographical area of focus, because they were either conceptual papers describing water security frameworks or literature review papers such as Bichai et al. [24], UN water [4]. The plotted map does not include studies done in multiple regions: North America and South

America [25]; Artic region with seven countries [26]; seven urban case studies selected from Asia, Europe, North America, and South America [27]; and 27 sites in 21 low-and middle-income countries across Africa, Asia, the Middle East, and the Americas [28].

**Figure 2.** Systematic review by publication date.

**Figure 3.** Systematic review by study locations (countries).

#### *3.2. Urban vs. Rural Focus*

Here, all the reviewed papers are further categorized based on their focus on rural or urban areas. 49 percent (*n* = 38) of the studies had a focus on rural areas, urban areas, or both rural and urban areas. The majority focused on urban areas (*n* = 22), followed by rural (*n* = 13), and finally papers focusing on both urban and rural areas (*n* = 3) (Figure 4). Papers dealing with rural areas mainly emphasized accessibility, availability, pollution, lack of awareness, poor governance, etc., as key hurdles for achieving water security. On the other hand, the papers focusing on urban areas mainly emphasized water infrastructure-related issues such as non-revenue loss and leakage from supply pipes, pollution, poor governance, flooding, climate change, etc., as key drivers for water insecurity. Finally, papers falling under the mixed category, deal with the coastal areas or river basins including both rural and urban sites. On the other hand, 51% of the papers did not have any focus area, they were either literature review papers or conceptual papers.

**Figure 4.** Systematic review by the focus of the study.

#### *3.3. Analytical Approach*

To understand the types of analytical approaches used in relation to water security frameworks, we grouped the reviewed studies based on their methodology used for analysis. From this, we found that all the analytical approaches could be classified into four major categories: big data analysis, literature review, qualitative analysis, and quantitative analysis (Figure 5). Around 16% of studies (6 of 77) used big data analysis, e.g., analyzing data from the national census or the global water data portal; 18% of the papers used qualitative analysis to analyze data from household surveys and key informants' interviews. Studies using a literature review as the principle analysis method accounted for 26% of all papers that contained the study of national and international reports, articles, local governmental reports, and case studies. Finally, 40% (the largest percentage) of the papers used quantitative analysis such as numerical simulations, statistical analysis of water quality data, machine-learning (e.g., neural network) analysis, remote sensing, and GIS- based analysis. The reason for quantitative analysis being the most dominant one is possibly due to the advancement of different tools and technologies for analyzing water quality and quantity. Also, many countries have become committed to achieving SDGs, and for this they are enhancing the monitoring activities of their precious water resources. However, for many developing countries, in absence of any past data, it is mandatory to do the baseline studies to get a clear picture about the current status and hence helpful take any timely measures.

**Figure 5.** Systematic review by study methods/approach.

#### *3.4. Water Security Dimensions*

All of the reviewed papers used multiple indicators or variables to measure water security under a different framework. All the variables and indicators were categorized under 11 dimensions in this study, and the result is shown in Figure 6. According to the number of appearances, the order of different dimensions considered in these papers are, namely public health > water quality > availability > policy and governance > ecosystem > socio-economic > water quantity = accessibility > risk/hazards > infrastructure and technology > sanitation and hygiene. Also, a summary of the list of reviewed papers and their association with different water security dimensions is presented in Table S1. Although health appeared as the most common dimension in these reviewed papers (51 percent of studies, *n* = 39), number of papers measuring direct health impacts such as incidence rates of water borne diseases, were still quite low (n = 14), which highlights the lack of priority being given to health-related issues when framing water security frameworks. Moreover, only a few papers discussed indirect health effects such as anxiety and stress, where water scarcity plays a mediating effect [18,29,30]. Most of the papers discussed direct health effects, which included issues such as the presence of different contaminants and pathogens which cause adverse health effects. The next dimension is water quality followed by availability with 47% and 34% of the share among the papers reviewed in this study [25,31,32]. Here, for the water quality component, most of the papers discussed different contaminants with grave health concerns and different approaches to monitor and manage them to achieve water security. A majority of these papers also discussed health aspects, hence they both share a large number of common papers in this graph. When talking about availability, this is more about water scarcity due to

geographical or climatic conditions such as arid regions and highlighting the different possible options for water resource management. The next dominant factor is policy and governance with 26% of papers covering it. It is evident especially from developing countries that poor policy and governance leads to water insecurity whether it is related to wastewater management in a city [2], or that poor policy related to water security based on time and distance to fetch water, often lead to stress and anxiety [33]. The fifth dimension is the ecosystem which appeared in 25% of the reviewed papers. The main idea to bring ecosystem in the discussion here is that an ecosystem-based approach must be adopted to manage not only water security but human well-being in any particular region [34]. The sixth dimension found in this study is socio-economic with an appearance in 22% of the reviewed papers. Here, the socio-economic dimension reflects on water inadequacy for people living in densely populated areas or informal settlements due to poor water systems or a poor capacity to access the available water [35–37]. The next few dimensions from seventh to the tenth rank, such as accessibility, water quantity, risk/hazard, infrastructure, and technology carries approximately similar occurrences in the reviewed papers [38–41]. These dimensions mainly discuss the effect of rapid global changes viz. climate change led to extreme weather conditions such as flooding or drought, on different water-related infrastructure, water accessibility, and water quantity. The last dimension i.e., sanitation and hygiene appeared in about 10% of the reviewed papers. The paper discussing sanitation and hygiene under a water security framework highlights the relation between poor water availability and sanitation and ultimately its impact on health whether its health of people or the ecosystem [42]. The main reason behind these low occurrences despite being a critical element of water security is that sanitation and hygiene are separately being discussed under the topic of Water, Sanitation, and Health (WASH). However, our goal here is to relate these dimensions under the umbrella of the water security framework.

**Figure 6.** Summary of different water security dimensions.

Among different frameworks reviewed in this study, the water security framework reported by [31], which is also called the DECS framework (Drinking water, Ecosystem, Climate change, and water-related hazards, and Socioeconomic aspects) adopted from the United Nations task force on water security, covered almost all dimensions, followed by Urban Water Security (UWS) framework by Romero-Lankao and Gantz and Urban Water Security Index (UWSI) [43]. On the other hand, frameworks that have widely covered the public health perspectives were the biocultural model of household water insecurity [28]; DECS UWS Framework [31]; UWSI [43]; HWIAS [44].

#### *3.5. Public Health*

This category represents both direct and indirect health impacts. According to the World Health Organization [45], health is defined as the state of complete physical, mental and social well-being and not merely the absence of diseases or infirmity. In this review, direct health impacts were considered to be the state free from water-borne diseases or the health impacts caused by the intake of water. Indirect health impacts were considered to be the mediating factors such as the accessibility to adequate quantities of acceptable quality water for physical and mental well-being. As mentioned, a total of 39 papers dealt with public health (both direct and indirect) issues. The result of direct health impacts is shown in Figure 7.

### **+HDOWKLVVXHVUHODWHGWRZDWHULQVHFXULW\**

**Figure 7.** Summary of direct health issues related to water insecurity found in reviewed papers.

Among direct health impacts, physical and mental health were considered. In physical health, water-borne diseases (diarrhea) were most common, considered by 14 papers. However, only 5 among the reviewed frameworks mentioned the inclusion of the incidence rate of diseases as a crucial variable to measure water security [31,46–50]. This was followed

by carcinogenic diseases caused by the presence of different pollutants such as heavy metals, including Cd, Pb, etc. [51] and finally skin diseases because of the presence of Arsenic [52]. On the other hand, mental health impacts such as anxiety and water stress appeared in 12 papers, i.e., 16% of the total reviewed papers. Experienced anxieties from water issues are strongly linked to household water needs not being met, time investments required for fetching water, suspected waterborne sickness, and household size [18,29].

Indirect health impacts or the mediating factors were considered by 25 papers. Aboelnga et al. [31] presented the DECS framework which has one of the dimensions as "drinking water and human wellbeing", which includes the sub-indicators such as water availability; diversity of water and energy source; consumption; reliability, water quality, accessibility, adequacy, equity, water bodies' and dependency ratio [47]. Similarly, the water-energyfood nexus framework by Marttunen et al. [20] has one of the dimensions as "human health and well-being" that includes the indicators such as quality and quantity of drinking water, sanitation, and hygiene, recreational opportunities. Similarly, water quality parameters such as heavy metals and microorganisms possess health threats. High Mg intake can cause hypermagnesemia; high Ca intake can cause cholesterol, muscle cramps, and kidney stones; high hard water intake can cause eczema, intestinal problems, and loss of fertility; high fluoride intake can cause fluorosis and osteosarcoma; and high nitrate intake can cause methemoglobinemia [39,53–55] and diseases related to the presence of microorganisms such as E. coli and fecal coliform can cause serious waterborne infectious diseases [44,46,56].

Table 1 shows how we use the term 'human health' while measuring water security as a whole. On one hand, water security measurement is limited to the provision of safe, adequate water supply and sanitation facilities, and on the other hand, the waterborne morbidity and mortality rates are also taken into consideration to achieve water security. The incident rate of waterborne diseases (particularly diarrhea), which is measured in cases per 100,000 population per year, is commonly considered to be one of the indicators of water security [26,31,46–48]. Carcinogenic diseases are measured by checking the prevalence of diseases such as skin malignancy [57]; carcinogenic risks are predicted through hydrochemical evaluation [51]; and mental health issues are often measured through self-reported items and behavioral manifestations [29,44]. Measuring the public's health is an important step in focusing attention and resources on improving health, and slowing the nation's declining quality of life, which is threatening the country's future [58].

**Table 1.** Public health measurement in water security.


Having clean water provision may not define good human health and having contaminated water may not always mean bad health of a population. To support this statement, the public health dimension (water-borne diseases) had a poor score (1) despite the excellent accessibility to drinking water [31]. It was correlated with poor access to hygiene, and with the intermittent water supply where there is the possibility of microbial regrowth due to static conditions. In contrast, despite the evidence of microbial contamination in the city's drinking water, incidences of waterborne diseases were found to be the lowest [46], attributed to the good hygiene practices by residents and public awareness regarding disinfection of water before drinking.

#### **4. Discussion**

Water is a basic need and is fundamental to life and health. Drinking water supply and sanitation are among the essential components of primary health care [59,60]. All people must have access to at least a satisfactory level of water in terms of adequacy, safety, and accessibility because just improving access to clean drinking water reduces a major burden on human health [12]. Depending upon climate, a person's physiology, social culture, and norms, the Sphere Standards suggest at least 15 L of water per day per person for basic survival [61]. It further elaborates that the maximum distance between any household and the nearest water point is 500 m; queueing time at a water source is no more than 15 min, and filling a 20-L container takes no more than three minutes [61]. Yet, every day, women and girls are estimated to spend 200 million hours hauling water around the world [8].

During the Covid19 pandemic, where handwashing is crucial to reduce infection, a Household water Insecurity Scale (HWIS) study showed that many households in low- and middle-income countries were not able to wash hands due to lack of basic handwashing facilities [17,62]. This reveals that significant investments in water infrastructure, water governance, promotion of knowledge, and behavioral changes are crucial [62,63].

Apart from the existing conditions, there are occasional conditions such as disasters, natural or man-made that affect safe water availability; accessibility; reliability; and adequacy, consequently worsening physical and mental health. A study by Rosinger et al. [64] after a historic flood found a higher dehydration prevalence among children in households with high water insecurity. Dehydration, on the other hand, has mental health impacts such as anxiety and depression [65]; mood effects [66]; tension and fatigue [67]; tension, depression, and confusion [30]; and short sleep duration [64]. A case from Haiti backs up theories that suggest household water insecurity plays a central, influential role as a potential driver of common mental illness in households through direct and indirect pathways such as food insecurity and sanitation [68].

Water-borne outbreaks could be minimized if the water is treated before drinking. A study by Carlton et al. [69] had an interesting finding that good sanitation, hygiene, and social cohesion did not modify the relationship between heavy rainfall events and diarrhea, instead of drinking water treatment by households was the factor to reduce the diarrheal events. Thus, they emphasized adopting water treatment behavior as a climatic adaptation to reduce climate vulnerability. Furthermore, even if there is a good WASH intervention, if other factors such as climatic variability, ecosystem, and other factors are not considered, there are very few chances to prevent frequent occurrences of water-borne diseases [69]. This evidence clearly shows that just having good access to drinking water or with good WASH services does not always mean good health. Therefore, measuring the direct physical and mental health impacts caused by the intake of water distributed would give justice to dimensions of water security for having a sustainable healthy livelihood.

This study addresses a gap in how we perceive health while measuring water security. Health, in medical discipline especially by doctors and nurses, is defined as the absence of diseases or infirmity, while health in water disciplines can be ecological health and the mediating factors for health. On one hand, health depends on hygienic behavior, and on the other hand, it depends on environmental conditions. Under environmental pressures such as climate change and other factors, the risks of waterborne diseases tend to increase, so much effort is being intervened to supply adequate safe water, which then is known as water security, while health professionals look after the morbidity and mortality rates, and conclude that water security is not achieved despite advancements in science and technology and water security measures. The biohazard 'Covid19' is another example that reflects the urgent call for water security. Studies also concluded that the household culture, norms, and how people treat water before consumption affects the value measured. This gap should be bridged by emphasizing more local and household surveys with the inclusion of health indicators such as households with water-borne diseases, hygiene, and sanitation both in routine and disaster periods for sustainable human security. Also, a

specific health-specific water security framework is imperative for dealing with issues arising from public health.

#### **5. Conclusions**

This study reports the water security frameworks and the place for health in them. Asia is the main hotspot for water security issues owing to rapid population growth, urbanization, and extreme weather conditions due to climate change. Mental health issues such as stress caused by poor accessibility and availability (in terms of time and distance) is a big determinant when framing water security frameworks, particularly in developing nations. Water-borne diseases due to poor water quality and sanitation play a major role in determining the water security framework for countries with poor governance on water and sanitation. Among different health issues, diarrhea is the most prevalent one considered for developing a water security framework because of poor water quality, especially the presence of biological pollutants. Although water security is a concept with several aspects and dimensions, public health is often not integrated into water security frameworks. More local and household surveys should be emphasized, with the inclusion of health indicators such as the percentage of households with water-borne diseases, hygiene, and sanitation both in routine and disaster periods for sustainable human security. As an important implication, this study provides knowledge and information of public health indicators in the available water security frameworks. This information is important for scientific communities, managers, policy planners, and stakeholders not only to conceptualize water security in a variety of meanings but also to measure water-related health issues for a population and its relation to other socio-environmental, provisional, and technical issues commonly prevailing in the human society. For the future, this study emphasizes developing comprehensive ways to refine the public health indicators at a ground level, to measure the significant burden that water insecurity places on human health. Similarly, a holistic approach with regular monitoring and future prediction of water resources and designing management measures on a timely basis are very much needed. Nexus approaches are needed, considering aspects of water-food-health-energy [20] or socio-hydrology [18] to achieve this very complex issue of water security and human well-being.

**Supplementary Materials:** The following are available online at https://www.mdpi.com/article/ 10.3390/w13101365/s1, Table S1: List of reviewed papers (from the Scopus search) associated with different water security dimensions.

**Author Contributions:** Conceptualization: P.K., S.P.; methodology: P.K., S.P., R.D.; formal analysis: P.K., S.P.; investigation: P.K., S.P.; writing—original draft preparation: P.K., S.P.; writing—review and editing: P.K., R.D., B.A.J., R.S., R.A., B.K.M., S.K. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Acknowledgments:** Authors also want to acknowledge the support from the Asia-Pacific Network for Global Change Research (APN) under Collaborative Regional Research Programme (CRRP) project with project reference number CRRP2019-01MY-Kumar, to accomplish this research work.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


## *Review* **Water Security in a Changing Environment: Concept, Challenges and Solutions**

**Binaya Kumar Mishra 1, Pankaj Kumar 2,\*, Chitresh Saraswat 3, Shamik Chakraborty <sup>4</sup> and Arjun Gautam <sup>1</sup>**


**Abstract:** Water is of vital and critical importance to ecosystems and human societies. The effects of human activities on land and water are now large and extensive. These reflect physical changes to the environment. Global change such as urbanization, population growth, socioeconomic change, evolving energy needs, and climate change have put unprecedented pressure on water resources systems. It is argued that achieving water security throughout the world is the key to sustainable development. Studies on holistic view with persistently changing dimensions is in its infancy. This study focuses on narrative review work for giving a comprehensive insight on the concept of water security, its evolution with recent environmental changes (e.g., urbanization, socioeconomic, etc.) and various implications. Finally, it presents different sustainable solutions to achieve water security. Broadly, water security evolves from ensuring reliable access of enough safe water for every person (at an affordable price where market mechanisms are involved) to lead a healthy and productive life, including that of future generations. The constraints on water availability and water quality threaten secured access to water resources for different uses. Despite recent progress in developing new strategies, practices and technologies for water resource management, their dissemination and implementation has been limited. A comprehensive sustainable approach to address water security challenges requires connecting social, economic, and environmental systems at multiple scales. This paper captures the persistently changing dimensions and new paradigms of water security providing a holistic view including a wide range of sustainable solutions to address the water challenges.

**Keywords:** water security; water scarcity; climate change; IWRM; socioeconomic changes; sustainable development

#### **1. Introduction**

Water is the foundation of life and necessity for everyone. However, it is becoming an increasingly scarce and degraded natural resource for millions of the world's population. Adequate water, which is necessary for various uses for a rapidly growing population, is one of the major challenges in recent years. It is a critical issue as the increase in food production to meet the future population will have to be achieved with the same water resources. Growing populations and climate change are added burdens to the global water crisis. More than 1.1 billion people have inadequate access to clean drinking water globally, and approximately 2.6 billion people lack basic sanitation facilities [1,2]. Water stress is increasing rapidly especially in developing nations of the world. According to the United Nations [3], global water use over the last century has been growing at twice the rate of population increase. As a result, approximately 1.2 billion people live in areas of physical water scarcity, where supply of water is not enough to meet the demand [4]. Apart from

**Citation:** Mishra, B.K.; Kumar, P.; Saraswat, C.; Chakraborty, S.; Gautam, A. Water Security in a Changing Environment: Concept, Challenges and Solutions. *Water* **2021**, *13*, 490. https://doi.org/10.3390/ w13040490

Academic Editor: Richard C. Smardon Received: 7 January 2021 Accepted: 9 February 2021 Published: 14 February 2021

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

physical scarcity, economic scarcity is another major issue for water insecurity. As of now, about 1.6 billion people face economic water scarcity, where people do not have enough financial means to access existing water sources. Lack of safe water access is gradually becoming a crisis for millions of people around the world that is responsible for poor health, destruction of livelihoods, and unnecessary suffering for the poor [5].

Water shortages are the most pressing challenge for socioeconomic and human development in general. Water shortages can lead to ecosystem degradation, worsening health and destruction of livelihood [6]. Increasing human pressure threatens the ability to provide adequate water resources and functioning of ecosystem services in the arid and semiarid regions and are particularly vulnerable to climate and land changes. As the human population grows and economic activity grows, water degradation has become a global concern [7]. Poor water quality, which makes water unfit for use, has multiple health and environmental consequences, and further reduces water availability. Contamination of the surface and groundwater is becoming one of the biggest threats to the available fresh water.

Today, more than half of the global population reside in urban areas [3]. With change in demography characterized by massive migration into cities, it is projected to further increase in percentage of urban population. Urban water supply systems for various applications as well as wastewater management for the increasing population is a serious threat, especially in developing countries. These cities have not been able to provide minimum water services to their growing population. Considering the urbanization pattern, it is urgent to improve water supply and wastewater treatment systems. These components should be seriously incorporated into urban planning.

A brief description of population and share of freshwater availability across different continents is shown in Figure 1 to highlight the issue of water scarcity.

Increase in water-related disasters is another important issue in the context of global change [8]. The number of deaths and economic damage caused by water-related disasters such as floods, droughts, landslides, and land subsidence has increased dramatically. Climate change and variability, land use changes, urbanization, migration patterns, energy problems, and food production caused by demographic change and economic development can exacerbate more uncertain risks.

Flooding is one of the most damaging natural disasters in the world. Floods are often seen as a natural phenomenon due to extreme weather events. However, in practice, human activity changes the environment in multiple ways, changes the water cycle, and hence more flooding. Therefore, flood risk and flood risk management are closely related to human activities. The impact of land-use change includes not only urbanization, but also the development and consolidation of agriculture [9]. Land-use policy has been a key factor in permitting urban developments in areas of risk. Flood risk results from extreme events, changes in the natural environment, and poor disaster management institutions which have the ability to reduce and manage risks.

Similarly, drought has multiple physical and social aspects. Lack of precipitation alters water resources and agriculture systems, and the impact can be severe, depending on the resilience of local communities and populations. Tensions between competing water use further worsen due to conflict between human use and environmental flow requirements [10]. Drought can constrain the multiple societal uses of water, including energy production, at local and regional levels. Many people rely on groundwater for drinking water, food security, and sustainable living. Groundwater use has increased significantly over the past 50 years due to its better quality and easy availability even during droughts [11].

**Figure 1.** A brief description of population distribution and water availability around the world [1,3,8,12,13].

These challenges require further research, implementation of new science-based methodologies, and endorsement of principles of integrated water resources management which can sustainably address various water-related issues. It is important to understand and manage water quantity and quality worldwide, and especially in the developing world. Overcoming the water crisis remains one of the most critical challenges our generation is facing [12] and developing clean potable water, managing wastewater efficiently and providing basic sanitation facilities for sustainability and human progress [13,14]. The United Nations (UN) Sustainable Development Goals 2030 will not be possible without achieving a water secure world first.

While resource allocation and competition requirements are to represent the first set of water security challenges, the second major focus for water security is on extreme events. It is very important to design a wide range of sustainable solutions, which addresses various water problems. With increased concerns on the sustainable use of limited water resources, in recent years, policy makers, organizations, funding agencies, and individuals largely use the 'water security' term to express their opinions for solving various water-related problems. However, there is no consensus on framing of water security concepts for solving water problems in a sustainable manner. Water security employing different disciplines is proposed as a starting point for solving various water related problems.

In the past few years, constructive efforts have been made to improve water security issues. Water security includes the sustainable use and protection of water systems, protection against water-related hazards, sustainable development of water resources, and protection of water functions and services for humans and the environment [15].

There is a need for holistic approaches to address the water security challenges and inclusion of the social, economic, and environmental dimensions at multiple scales. The holistic approaches can act as a catalyst for progress in many sectors such as public health, energy security, climate resilience, poverty reduction, and accelerate the pace of achieving the Sustainable Development Goals (SDGs). Water security is important to understand and manage various challenges in the context of environmental change. The interface between communities of researchers, practitioners, and stakeholders is seen as increasingly important for the recognition and management of water security.

Lack of infrastructure and capacity development; weak and rigid governance systems, and lack of interdisciplinary approach are among the major reasons for the increase in solving various water-related problems. Framing the challenges of water security goes beyond single-issue indicators such as water stress. In a rapidly changing world, we are solving new problems with old solutions. The status quo is no longer enough, and conventional models will not be able to achieve water security issues. It is crucial to

shift from ad hoc and isolated water solutions to integrated water resources management approaches, which yield more sustainable and resilient systems. A new paradigm is therefore needed that considers alternative solutions for achieving water security. The paper highlights water security issues and sustainable solutions at different scales and presents good practices to address water security challenges. This paper aims to review various water related problems and challenges in the global change context, explore emerging paradigms of water security assessment, and finally seek sustainable solutions towards achieving water security.

Therefore, this paper is aimed to address key questions on water security as: (i) what is water security? (ii) What are various dimensions of water security? (iii) How can we assess water security? and (iv) What are different sustainable solutions to improve water security? Answers to these questions will be of great value to policy-makers, who are responsible for making well-informed decisions and investment in the field water management.

#### **2. Methodology**

For this study we carried out a narrative literature review. To carry out the literature review, we searched through keywords water security, water scarcity, climate change, integrated water resource management, and sustainable development to focus our study within the review questions (see Section 1). The Claivariate Analytics's Web of Science (WoS) was used to search for scientific literature and articles pertaining to the combination of keywords mentioned above from year 2000 to 2020. Web of Science was chosen as it is one of the world's largest scientific citation search platforms, has an extensive coverage of a wide spectrum of studies related to a topic of interest, and a frequent source for literature review based analysis [16]. A variety of articles were searched to ensure that the majority of the relevant articles and the arguments they capture have been identified. After completing the search, abstracts were read and articles that were common (duplicates) in the searched databases were discarded. All the remaining abstracts were then read to find an answer to our review questions. We did not include all the articles of the abstracts we reviewed because of the relevancy of the arguments in the abstract and articles they represent. We then read all the articles thoroughly, this included a total of 71 articles, which show a diverse line of arguments on the review question. We then synthesized the findings from this literature review into a narrative and integrated into two main types of streams of argument—problems and solutions of water security under changing environmental and socioeconomic context. A list of reviewed papers used to identify different dimensions for water security is shown in Appendix A. The whole study is described in the flowchart shown in Figure 2.

**Figure 2.** Flow chart explaining the work done in this study.

#### **3. Water Security: Concept and Evolution**

Water security is critical to achieving sustainable and comprehensive growth. A watersecure world uses the productive power of water and reduces its destructive impacts. It is a world where everyone has safe, affordable, clean water to live a healthy and productive life. It is a world where communities are protected from floods, droughts, landslides, erosion, and water-borne diseases. Water security promotes environmental protection and social justice and deals with the consequences of poor water management. In general, several definitions have been proposed for water security, reflecting the desire to manage water resources. The 'UN agency on Water' defines the water security as "the capacity of a population to safeguard sustainable access to adequate quantities of water with acceptable quality necessary for sustaining livelihoods, human well-being, socio-economic development, ensuring protection against water- related disasters, and for preserving ecosystems in a climate of peace and political stability" [13]. Increasing water security lies in: (i) ensuring the availability of adequate and reliable water resources of acceptable quality to provide water services for all social and economic activity in a manner that is environmentally sustainable; (ii) mitigating water-related risks such as floods, droughts, and pollution; (iii) addressing the conflicts that may arise from disputes over shared waters, especially in situations of growing stress, and turning them into win–win solutions. Water security is emerging as a possible unified concept for water managers. Operationalizing the concept of water security means identifying its various aspects, setting goals, and exploring actions to achieve these goals.

In recent years, the focus of water security has become more diverse, expanding from water scarcity to clean water, ecosystem services and overall human wellbeing [17]. Conventional approaches focused on a single aspect and narrow perspective such as development studies tend to focus on national scales only, economists' main concerns are about the economic aspect of the problem, hydrologists often only focus on watershed scales, and the social scientists focused on research work around community only [17]. The new dimensions pledged to attain water security in a sustainable way with long-term vision, which proposes a range of sustainable solutions based on economic, environmental, and societal aspects [18].

The spatial and temporal considerations are important determinants for water security. Rijsberman [19] explained the supply problem when water is truly scarce in the physical sense, and demand problem when enough water is available but not used in a better or sustainable way. Hydrological extreme conditions such as floods and droughts can occur at the same location within the same year. Therefore, use of average available water cannot represent a measure of water scarcity or excess. In the monsoon season, many regions of Asia suffer from water scarcity while the average annual water resource availability appears to be abundant. Large countries like India can have water scarcity and flooding at the same time, but in different parts of the country. The situation of uneven distribution of water resources is going to be aggravated due to climate change. The understanding of water scarcity is vital as it affects the views on the most effective policies to deal with water crisis. The Intergovernmental Panel on Climate Change (IPCC) reports indicated that more than 87% of the climate change impact will be on water related infrastructure and increasing negative impacts of global warming is likely to increase the variations, frequency, and severity of weather such as extreme droughts and floods occurring [20]. On the global scale, a current water withdrawal is well below renewable water resources limit, but the concern is the high unpredictability of water resources in coming years [21]. Virtual water trade can be one of the effective options to address water scarcity, which is estimated around 1000 km3/year internationally although only a very small part of virtual water trade is utilized to compensate for water shortages. Another major challenge is pollution and deterioration of surface and ground water bodies in rapidly growing cities and elsewhere in the developing world. Understanding of causes and measures that lead to improvement of water quality degradation is limited. In order to address water quality degradation, several soft and hard measures need to be formulated at individual,

community, and institution level. It needs balance between technical and social approaches. Water quality is another major variable and its analysis is beneficial for security of the environment, human use, and understanding the water stress. Historical evolution of water security technologies is important to understand the present and future concept of water security (Figure 3). Urban regions required new strategies to cope with the transitioning phases of water requirements with the development of urban areas. Water supply for demand management was a concept in the water supply system in cities, which evolved and moved in the direction of water sensitive cities due to various factors. Various drivers are responsible for this transitioning phase of water such as rapid population growth and consumption patterns that use more water. To solve the emerging problem of water security, it is important to change the management response that appears in response to social and political factors [22].

**Figure 3.** Changing paradigms of Water Security and Transition Phase for cities (adapted from brown et al. 2008 [22]).

#### **4. Emerging Paradigms of Water Security**

Water Security embodies a complex, multidimensional and interdependent set of issues. With increasing pressures on water resources, there is heightened competition for the water uses at local, regional, and international scales, both between diverse sectors of the economy and jurisdictions. This comprises basic societal needs such as drinking water supply, irrigation, hydropower, and industrial uses. Achieving water security is also dependent on the water quality, which is a further key dimension of water use. Rivers are used to receive, transport, and dilute wastes, and intensification of human activities is putting increasing pressure on the quality of both surface waters and groundwater, with consequences for water resource availability for various uses. Water-related ecosystem functions, with their dependence on water quantity (and its temporal variability) and water quality is another critical dimension of water security.

Securing water for people and the environment is a necessary condition for sustainable growth, ending poverty and hunger, and achieving the SDGs. The dominant threats to water availability, quality, and supply vary geographically and over time. This entails achieving water security is not a dynamic goal, which evolves with changing dynamics. It is a dynamic process affected by changing climate, political set up, economic growth, and resource degradation. Moreover, as social, cultural, political, economic priorities, and values change, the goal for achieving water security evolves with them. In this background, the study argued for evaluating water security challenges under emerging paradigms and seeking the solutions.

Paradigm is a concept of envisioning the future of societal interaction with the environment based on the shared assumptions and values [23]. The emerging paradigms are significant in the context of continuous shifts in societal interaction with natural resources such as water. In order to bring holistic solutions to water security, the nature and characteristics of paradigm changes are necessary. Historically, paradigm shifts are seen as a continuous and necessary part of policy making. The important question that arises here is why there is a need to rethink water security under emerging or new paradigms. Societal interactions and values around water are continuously changing. For example, the shift from Millennium Development Goals (MDGs) to the SDGs, the focus of the water security concept has shifted from only water supply and demand in cities towards the perception of water as an economic resource shared between countries. The paradigm shift in water emphasizes on how societies are valuing water as a resource and support this transition. This shift comprises water governance, which is the capacity of governments to manage water equitably and efficiently, including across borders [24]. Due to increased economic development and climate change the uncertainty is increased which impacted the interactions of society with water resources. In the traditional paradigms, the water crisis is generally considered as technology related problems but under emerging paradigms focus is shifted towards recycle and reuse of water, considering waste and stormwater as resources, managing demand effectively, promoting green infrastructure, increasing community and stakeholder participation, effective governance, and multidisciplinary approach to achieve water security.

The four different paradigms shifts are identified in this paper to evaluate the water security and seek the solutions to achieve the goal. In changing context and challenges, the new approaches to govern the water is suggested by Huitema et al. [25], are the adaptive water governance and polycentric approaches to govern. Another perspective of Integrated water resource management (IWRM) is popular among the developing nations, how the IWRM evolves in current perspective. The nature-based solutions perspective is gaining popularity worldwide to achieve water security and still many scholars focus on the combination of hard/soft approaches to achieve water security (see Section 5). The paradigm shift in the water sector constitutes how water is managed in the current context under different challenges and transitioning the way of managing water towards diversifying water resources and building resilient infrastructure. Shift in financing the water sector is significant in emerging paradigms where engaging the private sector partnerships and reducing the nonrevenue water is in focus. Collaboration at different scales through regional and national cooperation and agreements are helpful in shifting towards system thinking approaches. This study envisioned the challenges and solutions to achieve water security under emerging paradigms in a changing environment.

#### **5. Water Security Assessment and Indicators**

Water security captures the complex concept of overall water management with resource conservation and its use [26]. Water security should be represented by indicators to promote its quantification. There are different kinds of water scarcity indicators proposed by various studies and explained in literature such as water stress indicator or Falkenmark indicator, water resources vulnerability index, economic water scarcity index, and water poverty index, among many others. There are several advantages of translating water security into numerical terms to encourage clarity and establish a common understanding of a concept around which there currently exists substantial ambiguity. This helps to facilitate discussion on the presence or absence of water security, or the scale and threshold for evaluating the degree of water security. This also assesses the extent to which water security on the ground has been achieved in various locations.

The treatment of wastewater is a very important aspect of water security. Historically, wastewater was considered as waste only, although it could be a valuable resource. If treated properly, wastewater can be reused and contribute to lesser pollution in water bodies. The recycling of water is the concept of reusing the treated wastewater or stormwater

for many useful purposes, such as irrigation, toilet flushing, needs of industries, and in some aspect for ground water recharge [27,28]. Recycled water or water reuse offers many kinds of resources and financial savings [29] and if this can be tailored to meet the quality standard required for the water use, then the recycled water can be considered as a vital resource because it offers series of benefits such as useful for irrigation, cooling water for power plants and refineries, toilet flushing at household level, controlling the dust in the city, mixing and preparing cement during construction activities, beautification of artificial lakes and parks, and industrial processes. This provides us with ample reason to consider treatment of water as a sustainable solution for achieving water security.

Sources of uncertainty in water security assessment can be demonstrated by riskbased water security indicators, such as the uncertainty in the climate model outputs. The IPCC report indicated that climate change is increasing the frequency of extreme weather conditions like flood, drought, etc. More than 87% of the climate change impact will be on water related infrastructure [20]. These indicators are important in analysis of risks based on what if scenarios, which provides the essential evidence to enable options between alternative courses of action. The risk analysis explores the range of likely future situations ranging from business as usual to extremely unlikely conditions [30]. Decision making process involves choices between different courses of actions counting their benefits in terms of risk reduction or cost–benefit ratio.

Scale is critical in assessing water security [31]. National level assessments make it difficult to take action at operationalization level. Agriculture dominates water use in the Asia-Pacific region, but focuses on water productivity, which is often used as a means of improving production. Therefore, this indicator deals with the available water, and how to use, for example, an increase in water storage, can become a more urgent issue in areas with economic water shortages. There is also a question mark over use of such indicators that explains the overall picture of the country, especially if watersheds cross national borders. Watershed based water security can be defined as "sustainable access on a watershed basis to adequate quantities of water of acceptable quality to ensure human and ecosystem health" [26].

It is possible that the region can be concluded water secure or insecure but interestingly, without the explicit environmental consideration the shared conclusion from water indicator's analysis that water security is achieved by the developed part of the world such as many countries in Europe, North America, Australia, and Japan, is a kind of flaw [19]. Creating and using indicators for water security has to be directed towards some management control or assessment action. Originally, a single indicator was mainly used to assess the quality of rivers for human use. Earlier, for example, a simple parameter indicator (e.g., Biochemical oxygen demand (BOD)) was sufficient as a river pollution control measure. As the industrial revolution began, various types of chemicals started spilling into rivers requiring multiple measurements. Thus, indicators were required to measure multiple effects and combine them into single-value indicators. A recent shift to water security has called for the addition of economic and ecosystem concerns. In addition, the largest consumer of water in most countries is irrigation agriculture. With the rapid growth of the global population, the fear of a decline in the supply of water available in food production, industry, and homes has become a major problem. This has led to a search for indicators of water resource security.

Water security clearly requires an integrated approach while recognizing and accepting that tradeoffs may be needed between the different water-using sectors. Indicators tend to be heuristic, and political and water specialists need to focus on those indicators which tell the most compelling story to other sectors if they are to encourage water-smart investments. Roger Calow [26] suggested five pillars of water security where indicators are water availability and access, risk and variability, equity and livelihoods, ecosystems and biodiversity, and institutions and actors [26]. Ian Makin [26] focused on national and regional measures of water security, rather than individual basins highlighting the importance of water management issues in 49 countries across the Asia and Pacific region

and the threat from many sources—population growth, urbanization, increasing water pollution, over-abstraction of groundwater, water-related disasters, and climate change.

Asian Water Development Outlook (AWDO) [1] provides a robust, pragmatic, and readily understood framework for assessing water security. This report presents a framework for the assessment of water security in five key dimensions: household water security, economic water security, urban water security, environmental water security, and resilience to water-related disasters. Status of water security in five dimensions represents inherent tension among water uses that emerge under increasing stress from competing water use sectors. These, when aggregated, provide an indicator of national and regional water security. The indicators (referred as dimensions) are seen as the means of measuring the outcomes of integrated water resources management. These provide a baseline for analyzing trends and the effects of policies and reforms that can be monitored and reported to stakeholders and offer a new way for leaders to look at the strengths and weaknesses of water resources management and service delivery. These indicators also indicate the direction and priority for increasing investment, improving governance, and expanding capacity in the water sector. Dunn and Bakker [32] developed a water security framework as a tool for improving governance for watersheds in Canada. This is in contrast to others who seek to develop national or regional indicators describing the challenge of developing and applying indicators at the watershed level that were originally designed for national or regional application and question their relevance and sensitivity for use at a community level and for including socioeconomic considerations. However, considering the importance of water quality and transboundary water resource management, this study explained water security based on seven dimensions that are shown in Figure 4.

**Figure 4.** Water security dimensions (based on the Appendix A).

#### **6. Sustainable Solutions**

Given global changes and its potential impacts water security is a growing concern. It touches upon all aspects of life and requires a holistic approach, which actively integrates social, cultural, and economic perspectives, scientific and technical solutions, and attention to societal dynamics. The complexities in water security point out that there will be different solutions for managing water scarcity at different spaces and times. To address water security, interdisciplinary collaborations are required across sectors, communities, and political borders to manage the competition or conflicts over water resources. Here, sustainable water management is a key which focuses on the conjunctive and efficient use of different water resources and on water allocation strategies that build the economic and social returns and enhance the water productivity. In addition, there is a need for a special focus on equity in access to water as well and social impacts of water allocation policies.

Based on the complex and intricate nature of water security, its dimension and different paradigms as mentioned above, this section advocates various sustainable solutions to achieve water security under three themes. A summary for reviewed papers supporting ideas for these three different themes of solutions to achieve water security is shown in Table 1.

**Table 1.** List of reviewed papers used to find water security solutions under following three different themes.


#### *6.1. Polycentric and Adaptive Governance*

Water governance becomes a sustainable solution when it safeguards ecosystems yet is able to consider social and economic wellbeing of people [33]. Governance refers not only to national level water legislation, regulations and institutions, but also the processes to promote stakeholder or community participation in designing water and sanitation systems and empowering communities with knowledge by increasing their ability to make decisions about the management systems. Restructuring of water governance methods refer to the social mobilization and actions designed in promotion of ownership, capacity building, coinvestment, willingness to pay for services, and incentives for participation at the community level. Van Rijswick et al. [34] recognized several factors important for sustainable water governance. These are knowledge on water systems, monitoring and enforcement, values, principles, and policy discourses, responsibility, authority and means, stakeholder involvement, conflict resolution capability, tradeoffs between social objectives such as allocation, regulation and agreements, and financial arrangements. These can be taken as a roadmap for sustainable water governance. Besides, the water governance solutions also promote gender equality in decision making [35]. It determines the relevant roles for the government entities to ensure the delivery of water and sanitation and keep checks on public and private players to meet the required needs. Building sustainable governance as solutions towards water security is a process, which is very effective in correcting market distortions, incentives, and adjustments to affordable pricing.

The water sector is considered underperforming and requires massive investment in infrastructure building and developing capacity. The complexity of the decision-making system, inability to receive timely information, conflicts of water rights (vertical and horizontal integration), poor coordination and interactions, and lack of holistic planning are the reasons and important challenges of water governance [36].

To deal with this complexity and scale of governance challenge for water security, here we would especially like to focus on polycentric governance. Polycentric means that water management plans and policies should be framed and agreed by all relevant stakeholders. In other words, both top-down and bottom-up approaches should be given weight. For adaptive governance, more emphasis will be on finding the best pathways to make robust water management plans amid rapid global changes. The benefit of such plans should reach the end users in terms of providing clean water, protection from hydrological hazards, and maintaining the health of the ecosystem.

In order to make a region more sustainable in terms of water resources, its locally available water resources must not be compromised by its socioeconomic activities. There is an urgent need for co-management, which includes the cycle of co-design, co-implementation, and co-delivery throughout the whole water cycle.


an integrated perspective in analyzing water related risk through socio-hydrological pathways is deemed essential for better understanding the action research and policy implication for sustainable water management [46].

#### *6.2. Combination of Hard and Soft Measures*


#### *6.3. Nature-Based Solutions*

Nature-based solutions are those that use or simulate natural processes to address contemporary challenges, including those associated with water management. Its objectives are, for instance, to increase water availability (soil water retention and groundwater recharge are nature-based solutions), to improve water quality (natural and artificial wetlands, and riparian forest buffers), or to reduce water-related disasters and climate change risks (restoration, flood plains, and roof gardens). In other words, nature-based solutions are ecological processes driven by vegetation and soil in forests, pastures, humid areas, as well as in agricultural and urban landscapes, which play an important role in water

movement, storage, and transformation. Nature-based solutions offer some of the most effective and sustainable ways to improve water security, and they frequently offer additional benefits for communities where they are implemented, including improved agriculture, job creation, and climate resilience. It can also play an important role in improving the supply and quality of water and reducing the impact of natural disasters.

Freshwater supply depends on healthy functioning of freshwater (riverine) ecosystems. However, studies are scarce that consider whole ecosystems such as a river [55]. Furthermore, most of the riverine systems are heavily altered anthropogenically, this is a big challenge that makes sustainable water resource management, miss vital 'pieces' or functions that relate to the diversity of the ecosystem that are needed to bring solutions that are sustainable. Freshwater ecosystems are often highly engineered and thus can undergo this act of missing the vital pieces of ecosystem diversity that is quite common, which eventually make the freshwater systems lose their resilience.

For example, freshwater systems such as rivers have undergone disconnection in the longitudinal, lateral, and vertical dimensions of the river systems [56], disrupting (and distorting) the freshwater ecosystems such as a river that continues to deliver freshwater related ecosystem benefits [56,57].

The degradation in resilience does not exclude the society that lives within the freshwater ecosystems (e.g., a river basin) causing decision-making gridlocks. For example, distorted governance on freshwater issues have occurred due to human interventions such as dams and barrages, changing of the river courses, covering the flow (and in many cases surrounding landscapes) with impervious surfaces have compromised diverse ecosystem functions and resilience in freshwater environments through decades of mismanagement. These gridlocks especially take place when high economic returns are available at the expense of functional diversity [58]. Therefore, keeping the freshwater ecosystems as diverse as possible can enhance this resilience, which can be used as a thread or anchor to bind the whole ecosystem together. Using the resilience concept as a binder can make the freshwater system undergo changes without changing its vital state and function. A key sustainable solution in this regard is binding through the available knowledge component in the freshwater landscape through stakeholder engagement that creates values in diverse ecosystem functions for capturing the dynamism and nonlinearity of the freshwater ecosystems (including its connection to other ecosystems) [59–62]. It is here that nature-based solutions (or landscape-based solutions) can work as eco-friendly technologies to enhance development of freshwater services, characterized by a number of low-cost, more flexible adaptation options in contrast to conventional 'grey' technologies, which the developing world, especially in urban areas, are now trying to implement [63].

Additionally, sustainable water management can be achieved by facilitation of a change in mindset towards landscape-based water management such as participatory watershed land use management (PWLM). The participatory approach can identify and engage champions within its offices and communities to promote long-term sustainable planning for urban water security [64–66]. It can be challenging at times due to low interest among citizens [67]. Pace of urbanization is important while introducing sustainable construction practices. Watershed management plans should be based on retrofitting models in collaboration with stakeholders and communities are essential. This should be based on physical analysis of existing water scarcity coping practices. Interactive design records are needed to adopt smart water management.

Another set of sustainable solutions include interlinked water, energy, and food components, with a balance between natural resource use and society's demand on such resources [67,68]. This forms a critical nexus essential for addressing challenges of sustainable development. Water, food, and energy are dependent on each other and share many comparable characteristics, including people's livelihoods, so a collective (i.e., a nexus) approach should be able to address this interdependency effectively.

The relationship between ecosystem and water security is mutually beneficial and a core component of sustainable solutions to water security as this ensures that sufficient

and good quality of freshwater is available to support the functioning of ecosystem (and healthy functioning of the ecosystem continues to deliver good quality and quantity of water). Unfortunately, understanding of the relationship between ecosystem and water security is still a new territory but stressed as an important component to achieve overall development in the society such as Sustainable Development Goals [69,70]. As ecosystems provide water required both in terms of quality and quantity for different communities, maintaining food security as well as to mitigate hydrological hazards necessary to achieve water security at a watershed level, it is important to ensure that ecosystems are conserved.

Traditional and local adaptation strategies for an ecosystem-based approach are needed as they are often based on 'time tested' methods and adaptation strategies for water management in the whole landscape, and not only its physical and chemical parameters as modern scientific methods try to achieve. Further investigation on local adaptation strategies is also needed for achieving water security and fighting effectively against the climate change impacts is necessary for policy makers [71]. For example, every village, town, or other type of human settlement unit can have a list of traditional and local adaptation strategies so that they can deliver at the time of acute water crisis. It is reported that the water and social agreement for a water sensitive city would be significantly different to that conventional urban water approaches and integrates the normative values of environmental protection, demand–supply security, flood control, human wellbeing, and economic sustainability [22].

Nature-based solutions are now fast becoming the center stage of solving diverse and complex problems related to water security. In 2018 for the first time, Brazil hosted the world launching of the United Nations World Water Development Report, which publicly stated the importance of nature-based solutions (NBS) for water. According to Stefan Uhlenbrook, the Coordinator and Director of the UN World Water Assessment Programme (WWAP), reservoirs, irrigation canals, and water treatment plants are not the only water management instruments at our disposal. "We can't wait for nature to solve all problems by itself, but we can get inspired and use it in favor of the planet."

#### **7. Conclusions**

Flooding, drought, inadequate access to drinking water, and sanitation are some of the well-known water problems across the globe. There is a need for sustainable solutions, which are appropriate for varying contexts, local consideration to societal values, which leverage the multiple uses and make use of synergies with management of other resources. As these problems are increasing across different regions and different scales, there is an urgency to take measures for the protection of the water and to improve legislation and public awareness in this field to find the optimum way to manage, protect, and serve our limited water resources, and enforce water pollution control and the protection of water by suggesting remediation alternatives to reduce or control the influence of the contamination.

This paper explored new paradigms and evolving definitions of water security, and presented a wide range of sustainable solutions to solve various water-related problems. Water security is fundamental to achieving any kind of sustainable economic and human development. The challenges of water security are unprecedented, and a new approach to provide the underpinning science for water security management is urgently needed by the global community. An integrative framing of water security should take place at the policy and governance level, where established priorities and decisions are taken with agreement of stakeholders. An integrative approach is likely to bring good water governance and set a new approach to sustainable water management. The evolving paradigm of achieving water security will be able to provide sufficient water for socioeconomic activities for domestic, industrial, and commercial purposes, and clean drinking water to meet basic needs at an affordable price with proper sanitation, while treating and collecting wastewater to curb water pollution. Various dimensions of achieving water security extend to protecting ecosystems and increasing the role of nature to sustain its own functioning and developing

ability to cope with changing conditions. It also deals with timely response to the risk of water related disasters such as droughts, floods, spreading of diseases, and pollution.

Attaining water security in a changing context is not a simple or 'one size fits all' solution. Expanding the portfolio of solutions from fully engineered systems to management systems based on capacity building, community awareness, managing the wetlands, and conservation of aquifers need to incorporate the natural processes to achieve desired results to attain a water secure future for human wellbeing. It addresses the impacts of human activities on water quantity and quality, aquatic ecosystems and climate, and the context of rapid economic growth and climate change. It can be concluded that water security has multiple and highly interconnected dimensions, and that each of these involves complex interactions between human society and the natural environment. In conclusion, achieving a water secure world requires balance between social, environmental, and economic components. It requires adequate integration of soft and hard measures such as in storing and transporting water and in protecting the resource itself.

**Author Contributions:** Conceptualization: B.K.M., P.K., C.S., S.C., A.G.; methodology: B.K.M., C.S., P.K., S.C.; formal analysis: B.K.M., P.K., C.S., S.C.; investigation: B.K.M., P.K., C.S., S.C.; writing original draft preparation: B.K.M., P.K., C.S., S.C.; writing—review and editing: B.K.M., P.K., C.S., S.C., A.G. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **Appendix A**

**Table A1.** List of reviewed papers and their relation with seven different dimensions of water security.



#### **Table A1.** *Cont.*


#### **Table A1.** *Cont.*


#### **Table A1.** *Cont.*

#### **References**


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