Next Article in Journal
Application of CityDrain3 in Flood Simulation of Sponge Polders: A Case Study of Kunshan, China
Previous Article in Journal
Water Poverty in Rural Communities of Arid Areas in China
 
 
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Review

A Review of Rainwater Harvesting in Malaysia: Prospects and Challenges

1
Department of Water and Environmental Engineering, Faculty of Civil Engineering, Universiti Teknologi Malaysia (UTM), Johor Bahru 81310, Johor, Malaysia
2
Centre for Environmental Sustainability and Water Security (IPASA), Research Institute for Sustainable Environment, Faculty of Civil Engineering, Universiti Teknologi Malaysia (UTM), Johor Bahru 81310, Johor, Malaysia
*
Author to whom correspondence should be addressed.
Water 2018, 10(4), 506; https://doi.org/10.3390/w10040506
Submission received: 5 March 2018 / Revised: 30 March 2018 / Accepted: 17 April 2018 / Published: 19 April 2018

Abstract

:
The mismatch between freshwater demand and its availability is a major problem that causes global water scarcity. The exploration and utilization of rainwater seem to be viable options for minimizing the aforementioned issue. This manuscript reviews the prospects and challenges of the rainwater harvesting system (RWHS) in Malaysia. Malaysia can be categorized as a country that has high annual rainfall, as well as high domestic water consumption. Thus, Malaysia is well positioned to harvest rainwater for both potable and non-potable uses. Although the RWH guidelines were issued in Malaysia in 1999, the implementation of RWHS as an alternative water resource is still very limited due to its long return on investment and poor public acceptance. Major future challenges on the implementation of RWHS in Malaysia are to achieve competitive cost, the wide application of commercial buildings, a cost effective treatment system, effective policy implementation, the application of green materials, public perception improvement, and reliable first flush technology. Some recommendations such as providing appropriate subsidies and limiting the use of piped water are necessary for implementing RWHS at wider scales.

1. Introduction

In the new global development, freshwater scarcity has become a central issue in sustainable development. It is obvious that this issue is becoming a threat, as well as the largest global risk in terms of its potential impact. The main driving forces for the rising global demand for freshwater are the increasing world population, improving living standards, changing consumption patterns, and the expansion of irrigated agriculture [1,2,3]. In addition, the mismatch between freshwater demand and availability is the essence of global water scarcity. Therefore, several studies have been carried out to assess global water scarcity in terms of physical, social, and economical aspects [1,4,5,6].
In order to reduce and minimize water scarcity consequences, the use of rainwater has been widely accepted as a reliable alternative. Studies on the rainwater harvesting system (RWHS), particularly on the techniques and treatment system, have increased significantly in recent years [7,8,9,10,11,12,13,14]. RWHS can be defined as the collection and storage of rainwater for use rather than to waste it as runoff. In general, RWHS techniques can be categorized into two types, namely surface runoff and roof top RWHS. The advantages of RWHS include potable water savings, the mitigation of flooding in urban catchments, and the reduction of nutrient loads to waterways. In addition, RWHS has other advantages in terms of a lower carbon footprint compared to other water supply systems and more efficient energy use because less pumping is required from source to consumer [11,15]. Moreover, RWHS has the potential to simultaneously address water scarcity problem and reduce dependency on domestic water supply [16].
The selected strategies on the benefit of RWHS are listed in Table 1. It is noted that RWHS have many benefits related to the economy, the environment, technology, and society. For economic benefits, annual domestic cost savings of up to $240 per house can be obtained when implementing the system [17]. In addition, RWHS was expected to be more economical for a higher water tariff [18]. In terms of the environmental benefits, a study in South Korea found that RWHS can reduce up to 10% of flood [19]. This is in line with another study that recommends that RWHS is less economical for water supply alone, unless it is also considered as flood control technology [20]. There is also the potential to delay the development of a new storage infrastructure, because RWHS can reduce domestic water demand [21]. For technology and social benefits, RWHS provides as an alternative water resource and reduces water-related health risks [22,23,24].
It is well established that RWHS is capable of reducing peak water demands on the urban water supply [25]. The implementation of RWHS in several areas in New South Wales, Australia has resulted in considerable savings of water from the main supply, even in relatively low rainfall areas [25]. The benefits of reduced volume and peak demand can be translated in terms of smaller infrastructure size and savings of operation and maintenance costs [26,27,28,29]. For instance, in a suburban area of Melbourne, the use of rainwater tanks can reduce up to 18% and 53% of the network pipe sizes and operational costs [27]. Moreover, a considerable reduction in operating costs and greenhouse gas emissions of regional water supply systems can also be obtained by implementing RWHS [25].
Since RWHS could potentially reduce dependency on the domestic water supply, this system has been implemented in various areas such as agricultural [34,35,36], residential [37,38,39,40,41,42,43,44,45,46,47], and commercial [7,16,48,49,50,51], as presented in Table 2. For residential buildings, high percentage reliability above 95% can be achieved by implementing RWHS for several counties such as Australia [52], USA [53], and Iran [54]. When RWHS is implemented for large roof and high water consumption such as commercial buildings, up to 37% reliability can be obtained [51]. For agricultural fields, the implementation of new techniques with rainwater involvement can improve the yields compared to conventional technique [35].
Also, various methods have been implemented to optimize RWHS [12,13,55]. Hudzori [56] proposed a mathematical model for optimizing water storage tank and water utility supply for RWHS using daily rainfall data in Nusajaya, Johor Bahru. According to Chiu et al. [57], optimum tank size and energy consumption are indicators of the reliability of the system and become economically feasible when both energy and water savings are addressed together. In addition, designing RWHS under different climatic regimes in Italy was also conducted [58]. Their study reported that the performance of RWHS can also be analyzed using demand fraction and the modified storage fraction. Various investigations that aim to implement RWHS in UK have also been conducted such as technical framework [59,60] and socio-technical practices [61,62]. Therefore, several innovations of RWHS by implementing gravity or non-gravity have been established in UK [60].
To encourage implementation of RWHS, several countries have issued legislations as presented in Table 3. For instance, the Japanese government offers subsidy and low interest loan to premises for RWHS installation [64]. Alternatively, rebates and tax exemptions are also provided to encourage the implementation of RWHS [65,66]. The Spainish and Belgian governments have mandated the implementation of RWHS for new buildings with a certain roof area [65]. The aforementioned facts reveal that the countries have paid attention to water management practices and serious sought to find an alternative water resource.
Malaysia is a tropical country that is relatively rich in water resources with an average annual rainfall of 2400 mm [71]. Although Malaysia has never experienced any serious water crisis in the past few decades, uneven distribution of rainfall over space and time has led to some areas suffering from dry spells, while others have been affected by major flooding. The aforementioned facts revealed that the use of rainwater for alternative water resources and flash flood reduction is crucial and has a high potential.

2. Water Issues in Malaysia

The future rainfall in several states in Malaysia is predicted to decrease due to climate change effects [72]. The predicted change in the rainfall regime would have serious water supply repercussions in highly populated urban areas [73]. In general, annual rainfall map in Malaysia is shown in Figure 1. For comprehensive knowledge, the frequent rain event in Malaysia ranges from 132 to 181 days/year as presented in Table 4. In addition, Figure 2a shows average annual non-revenue water levels over Malaysia from 2010 to 2016 with an average of 36% [74]. For various states in Malaysia, the lowest and highest non-revenue water levels are P. Pinang (19%) and Pahang (50%), respectively.
Moreover, Malaysia can be categorized as one of the countries that has high domestic water consumption, which ranges from 209 to 228 liters per capita per day (lcd) as shown in Figure 2b. The consumption is still above the recommended target by the World Health Organisation (WHO), which is 165 lcd [74]. In this context, Penang records the highest water domestic consumption, while Sabah is the lowest. Moreover, Malaysians use much more water than their neighbors, Singaporeans, which is only 143 lcd in 2017 [76]. Therefore, Malaysia may undergo a water shortage crisis in the foreseeable future if water consumption is not improved.
Although, in general, the water tariff in Malaysia is still low compared developed countries (see Table 5), the tariff shows increasing trend for all states. For instance, in Johor, the commercial water tariff has been increasing from RM0.37/m3 in 1965 to RM3.0 m3 in 2015 and is still predicted to increase further as presented in Figure 2c [77]. This situation might become problematic for developing countries including Malaysia, particularly for the poor who have to allocate a greater proportion of their income to getting clean water.
The water demand in Malaysia is observed to increase from 10.4 billion m3/year in 1998 to 12.1 billion m3/year in 2010 and is projected to increase further to 17.7 billion m3/year in 2050 [79]. It is well known that 97% of water supply in Malaysia is abstracted from surface water sources, primarily rivers [80]. Malaysia has 189 river basins (89 in Peninsular Malaysia, 78 in Sabah, and 22 in Sarawak). However, in some highly developed and populated areas such as in Selangor, Putrajaya, and Federal Territory of Kuala Lumpur, the river resources have been fully exploited [81]. Therefore, an alternative water resource should be introduced to reduce over dependence on river water and helping the poor to reduce the water bill.

3. Global Perspective of RWHS

RWHS can be defined as direct collection of rainwater from roof and other purpose-built catchments and the collection of sheet runoff from man-made ground or natural surface catchment and rock catchment for potable and non-potable uses. Studies on RWHS have been intensively carried out, since this system has several advantages for the environment and community [82,83,84,85,86,87,88,89,90,91]. Over the past four decades, the number of studies related to RWHS has increased exponentially as shown in Figure 3 based on a keyword ‘RWHS’ in Scopus database. At the time of this research, total publication related to the topic identified via keywords “rainwater harvesting” is 2000.
RWHS provides high quality water, reduces reliance on the piped water, and generally is cost effective. The RWHS can range in size from simple to large scale systems. An approach of RWHS collected from the roof of a building provides the practical and effective utilization of rainwater. RWHS can be applied for both small and large-scale premises, but certain criteria need to be satisfied before implementing the system.

4. RWHS in Malaysia

4.1. Policy

The severe drought in 1998, especially in Klang Valley, has triggered the Malaysian government to embark RWHS. Following this water crisis, the Ministry of Housing and Local Government has promoted houses to install rainwater collector. Therefore, the government has issued a guideline on installing a rainwater collection and utilization system in 1999. Following this, various initiatives in the form of policies and guidelines have been formulated by various agencies (Table 6). This is to facilitate the implementation of RWHS for residential and government buildings.
To support the program, several projects have been carried out by the Malaysian government (see Table 7). In addition, it can be seen from Table 7 that various RWHS projects such as underground and aboveground tanks have been implemented. Most RWHS projects in Malaysia use high-density polyethylene (HDPE) for the aboveground tanks. Total costs to install RWHS range from RM 20,000 to RM 350,000 depending on the size and type of building. The Malaysian government pays attention to RWHS as an alternative resource to reduce over dependence on river and other surface waters.

4.2. Study Trend

Since the launching of RWHS program in Malaysia, several studies have been carried out to support this initiative [55,95,96,97,98,99,100,101]. Until today, total publication related to the topic identified via keywords “RWHS” is 47 as presented in Table 8 [92]. Universiti Putra Malaysia, Universiti Kebangsaan Malaysia, University of Malaya, Universiti Teknologi MARA, and Universiti Teknologi Malaysia are the top five institutions publishing RWHS topic as listed in Table 9.
Sultana et al. [98] evaluated the effects of green roof on rainwater quality. In general, the quality of roof water is good and requires minimal treatment for dissolved oxygen (DO) and pH. Alternatively, Abdul Ghani et al. [97] analyzed rainfall to determine the potential of RWHS site in Kuantan, Pahang. The highest amount of rainfall was in December and the lowest in February. Moreover, Hamid and Nordin [102] observed the reliability of RWHS installation system at a university hostel in Shah Alam, Malaysia. It was estimated that the installation of RWHS would reduce usage of treated water by about 6500 m3 per year and save up to RM 10,460 per year.
Hashim et al. [55] proposed a simulation-based program for optimization of large-scale RWHS. Specifically, this study investigated the suitability of RWHS for a community of 200 houses with an average total daily water consumption of 160 m3. Their study found that the optimal size storage tank for a 20,000 m2 roof area is 160 m3 with 60% reliability. In addition, their study also confirmed that a significant water saving of up to 58% can be achieved using their proposed model. The estimated total cost for the system is USD 443,861 and expected life-span of 25 years. Shaheed and Mohtar [101] investigated suitability of the rainwater quality as alternative drinking water source in Selangor, Malaysia. Their study confirmed that the physio-chemical quality parameters such as pH, DO, TSS, COD, and NH3-N adhered to the drinking water standards permitted by the Malaysian authorities.
The above-mentioned works confirm that there is a need to promote RWHS at the biggest scale. In this context, the National Hydraulic Research Institute of Malaysia (NAHRIM) has collaborated with other government agencies such as DID, Department of Local Government, Universiti Teknologi Malaysia, Universiti Sains Malaysia, and Universiti Malaya to conduct research on RWHS. Presently, NAHRIM pursues research and development (R&D) of RWHS focusing on hydrologic and hydraulic design, system design and performance, installation and operational costs, and water quality aspects.

4.3. Benefit of RWHS

In general, the benefit of RWHS can be divided into two categories, namely, environmental and economic [31]. For environmental benefit, it can be used as alternative water supply to supplement piped water. When used at large scale, RWHS can help to reduce flash flood in urban area and minimize soil erosion, as well as to prevent pollutant from entering water bodies [52].
Specifically, the economic benefit of RWHS has been examined by several researchers as listed in Table 10. Since RWHS is very useful for non-potable water use, it has the potential to reduce bills. Financial viability analysis of the RWHS was assessed for single and multi-family buildings [65]. Their study found that the payback period of the RWHS investment was between 33 and 43 years, and 61 years for a 20 m3 tank for single and multi-family buildings, respectively. Rashidi Mehrabadi et al. [54] found that it was possible to supply about 75% of non-potable water demand by storing rainwater from larger roof areas in Iran. Since the benefit of RWHS is highly dependent on water usage, system design, rainfall, and other uncertainty variables, its evaluation of long-term performance is needed to better understand the effects of each variable on its benefits. This is very useful as a basis for designing the future RWHS.

4.4. RWHS Type

In Malaysia, several types of RWHS have been implemented, namely, backyard system, frontage system, and underground system as shown in Figure 4 [110]. Backyard and frontage systems are also established as ‘collection systems only’, because they have no distribution system. Backyard system is the most popular, because it is cheap and easy to install compared to other systems that require plumbing system. In this system, there are two approaches to locate the storage tank, either on the ground or elevated. Ground tank is widely-established for RWHS development in various countries such as Brazil [111], Australia [63], and Portugal [112], and continents such as Africa [113], while the elevated tank commonly consists of three levels of tank, namely, top, middle, and lower levels. The top-level tank is usually employed for water supply, while the middle and lower level tanks are used for storing the collected rainwater. For this system, metal and polyethylene tanks are normally used for elevated and ground tank, respectively.
For the frontage system, it adopts the same installation concept with backyard system. A modification is usually done by replacing the polyethylene tank using the reinforced concrete tank to facilitate the maintenance work. It is known that the concrete tank is more durable compared to polyethylene tank; thus, it makes it more economical over the long-term [110]. It is also noted that the use of concrete tank is relatively cheaper (up to 38% compared to polyethylene tanks [114]). As for the underground system, the cost, which includes a pump, was about RM1700 for small scale systems such as home consumption [110].

4.5. RWHS Software

Since a proper design of RWHS involves a lot of data and analysis, it is useful to use software to expedite the process. Therefore, several computer-based models have been developed and implemented such as the SimTanka2, Warwick calculator, and the Jomo Kenyatta University of Agriculture and Technology’s RWHS (JKUAT-RWH) calculator [115]. The SimTanka2 and Warwick calculator are developed to evaluate the optimal tank size of RWHS, whereas JKUAT-RWH calculator is used to estimate the reliability of the system by performing a long-term time series of daily rainfall. Alternatively, Yield After Spillage (YAS) software was designed to estimate the actual rainwater availability and storage conditions [116].
In Malaysia, the software development has been tackled by NAHRIM. Tanki Nahrim is a famous software for calculating the aforementioned analysis [117]. Hamid and Nordin [102] confirmed that software is reliable for evaluating the reliability of a RWHS in a university hostel in Shah Alam, Malaysia. This software was also used to estimate an optimum tank size of the RWHS in another nearby college [118]. However, this software has limitations such as the absence of an economic evaluation [55]. Therefore, a more complete RWHS software that integrates the physical design and economic benefits is crucially needed. This is highly beneficial for providing comprehensive knowledge and convenience to public in order to encourage the implementation of RWHS.

5. Future Challenges

5.1. Cost

The cost is still a problematic issue when applying RWHS for several areas. Initial cost and maintenance are still debatable with regards to how this system can be affordable for all societies, especially for people in the low income category. This limitation is associated with national income and the low awareness of the community. Although water tariff in Malaysia is deemed as one of the lowest compared to neighboring countries such as Singapore (2.39 USD/m3) and Indonesia (0.51 USD/m3), the cost to install the RWHS is estimated between USD 400 and USD 3000 [93].
In order to maximize the benefits, an optimum RWHS design is highly crucial. In addition, the material selection can also reduce the initial cost. Designing RWHS using gravity has the potential to reduce the operation and maintenance cost compared to that system with pumping operation. Moreover, the government may provide subsidies to encourage the public to install the system. Also, training and awareness campaigns are highly beneficial for enhancing the interest of the community.

5.2. Application

Currently, the application of RWHS in Malaysia is still limited to government buildings. The exploration of other potential buildings such as commercial buildings is interesting, since they usually has larger rooftop catchment area. For instance, total catchment area of 10,000 m2 can provide a potential rainwater collection of 23,000 m3 annually. Since rainwater quality is almost free from major contaminant [119], only minimum treatment is needed if it is to be used for domestic or cooling purposes.
Therefore, the savings from implementing RWHS in commercial buildings are more rewarding compared to small installations in houses, because the commercial water tariff is higher, and the water consumption is bigger. The benefits of installing RWHS are more attractive when it is implemented early during the design and construction phase as opposed to during the retrofitting of the existing building. Therefore, implementation of RWHS in the foreseeable future should be more intensively applied for large buildings.

5.3. Treatment System

Most of the existing RWHS is for non-potable uses, in which the water is used directly from the collection tank. Although rainwater in Malaysia is relatively clean from major contaminants, minimum treatment is still needed before it can be utilized for potable uses. Table 11 lists the roof rainwater quality in Malaysia [120]. It is obvious that some parameters such as turbidity, lead, fecal coliforms, and total coliforms are present above limit regulated by World Health Organization (WHO). The aforementioned facts reveal that a simple treatment still needs to be done before the rainwater can be widely used for potable uses.
Therefore, it is worthwhile incorporating a simple treatment system in order to maximize the economic benefit of RWHS. Although many methods such as disinfection [121], slow sand filtration [9], membrane filtration [122], pasteurization [9], ozonation [123], and adsorption [124,125] are possible, their cost and suitability are important to be consider. In order to maximize the investment benefits, a clear goal of constructing RWHS should be considered prior to installation.
The selection of rainwater treatment method has implications for the installation and maintenance costs. For instance, non-potable uses of harvested rainwater such as toilet flushing, landscape irrigation, and car washing do not require treatment. Conversely, the use of harvested rainwater for potable uses such as drinking, cooking, shower, and cloth washing needs a cost-effective treatment method. Treatment is also necessary when the harvested rainwater is used for chiller system. Therefore, it is crucial to provide a cheap treatment method to maximize its economic benefit. In addition, a simple treatment system with less maintenance has additional benefits for installation in rural areas. In this regard, filtration with pH adjustment (to ±pH 7) would be sufficient for treating rainwater for chiller system, whereas for domestic uses, additional treatment trough disinfection is necessary.

5.4. Rainfall Characteristics

The success of RWHS is greatly dependent on the quantity and temporal pattern of the rainfall. It was estimated that the percentage of reliability of RWHS for toilet flushing, laundry, and irrigation use increased from 40% to 71% for study locations having an average annual rainfall ranging from 743 mm to 1325 mm in Australia [63]. As listed in Table 4, average annual rainfall in Malaysia varies according to the region. For instance, Seremban and Kuantan have the lowest and the largest annual rainfall, which are 1901 mm and 2881 mm, respectively.
To maximize its benefit, the development of RHWS in Malaysia should consider their rainfall quantity. For a similar roof area and water consumption rate, the higher rainfall depth would be more reliable. Moreover, being located in the humid tropic region, the number of rainy days in Malaysia is high (138 days to 181 days/year). Thus, the use of RWHS should be maximized in order to have the biggest water savings in the reservoir that is to be used during dry period. Considering the spatial variation of rainfall in Malaysia, it is crucial to assess RWHS potential for various rainfall regions.

5.5. Policy

Although the Malaysian government has launched RWHS policy, the implementation has been mostly confined to public buildings, and bungalows and semi-detached houses. The DID Malaysia has been promoting RWHS projects for various types of buildings as listed in Table 7. For each project, either above or underground RWHS tanks were installed. Most of the projects installed HDPE tank except for National Zoo project, which used concrete tank. Depending on the tank size and category, the installation cost ranges from RM 20,000 to RM 400,000.
For future, the RWHS policy should be extended to all buildings with large roof area such as commercial buildings, which are expected to have a larger economic benefit. Unfortunately, the existing policy is still quite loose [93]. There is no mention of the minimum requirement of tank size in relation to roof area. In addition, commercial buildings are still not subjected to this policy. Therefore, a comprehensive study considering an optimum tank size according to the various roof sizes and climatic conditions in Malaysia should be carried out for foreseeable future as a scientific judgement before issuing a legal policy.

5.6. Material

Rainwater is relatively clean but can be contaminated by the roof materials and deposition on the roof surfaces. In older systems, the commonly used roof materials were steel, copper, aluminium, zinc, or tin. Overtime, the roof materials become rusty and were subjected to leaching by rainwater, which is normally quite acidic (about 5.6) [126]. Thus, it became a source of contaminant in the collected rainwater. In addition, application of paint, tar, glue, sealant, and other protective materials in order to lengthen the roof life span may contribute additional forms of contaminant. Moreover, there are various types of tanks depending on the materials being used such as polyethylene, concrete, galvanized steel, fiberglass, and stainless steel, which tend to rust overtime and could release certain chemicals.
These shortcomings could be overcome by introducing more inert and environmentally friendly materials. For this purpose, natural resources such as rattan, bamboo, and oil palm in the form of fibers or particles can be used as composite materials. Natural materials have been proven to have physical and mechanical properties that are comparable to synthetic materials [127]. Therefore, a comprehensive study by applying natural materials is needed crucially in Malaysia. This knowledge is useful to inform the public that better collected rainwater quality can be obtained using inert and environmentally friendly materials.

5.7. Public Perception

Despite various initiatives by the government to promote RWHS, acceptance among Malaysians is still unsatisfactory. One of the main reasons for the poor acceptance is because of low water tariff. At the moment, Malaysians are paying between RM 0.96 and RM 3.05 depending on the water supply service provider [77]. In addition, the average water tariff in Malaysia is among the lowest in the world (0.20 USD/m3) compared to neighboring country of Singapore (2.39 USD/m3) and developed countries such as Tokyo (2.0 USD/m3), Dubai (2.4 USD/m3), New York (3.1 USD/m3), Amsterdam (5.2 USD/m3), and Copenhagen (7.3 USD/m3) [128].
Malaysia is also blessed with abundant rainfall with rare occurrences of significant drought. This makes the general public feel that there is no necessity to explore other alternative water resources. It is evident from the high rate of domestic water consumption, ranging from 209 to 228 lcd as depicted in Figure 2b compared to best practice of 165 lcd as benchmarked by WHO [74]. Finally, the public is inadequately educated on the importance of rainwater utilization within the context of water demand management. Both strategies in terms of penalty and incentive are crucial for ensuring fuller implementation of rainwater harvesting at residential, commercial, and industrial premises. For instance, Singapore imposes penalty in the form of much higher tariff when a factory exceeds certain limit of water usage from public supply [129]. On the other hand, Malaysian government can offer incentive by providing rebate to premises owner who installs RWHS. In addition, a proper awareness program is necessary to educate the public on how RWHS can be implemented to reduce the dependency on domestic water supply.

5.8. First Flush Technology

One of challenges in using rainwater is to minimize pollution associated with the first flush. The source of contamination may come from leach out of roof materials, dry deposition, and bird droppings. Traditionally, this can be carried out by manually diverting the first flush from entering into the collection tank. However, this requires the personnel to be on standby. Figure 5 shows typical design of first flush device of RWHS. The existing flush systems still have weaknesses, because the first flush collector has to be emptied manually. In view of the frequent rain event in Malaysia ranging from 132 to 181 days/year as presented in Table 4, this manual removal is not practical, and the collected rainwater is exposed to contamination when the first flush collector is not emptied prior to the next storm event. Therefore, it is possible to automize the first flush by using floating system or mechanical devices.
In Malaysia, the rainfall duration is usually between 0.5 h to 3 h with averages dry period between rainfall ranging from 2.0 to 2.8 days [130]. However, rainfall duration during monsoon period (November to early January) in the east coast region of Peninsular Malaysia may prolong to several days. Automatic emptying of first flush collector is recommended when labor and investment costs are not an issue and high quality roof water is required. Nevertheless, manual emptying is more practical for small scale RWHS in order to minimize the investment cost. In this case, it is necessary to educate the public on the need to consistently empty the first flush collector to avoid possible contamination.

6. Recommendations to Encourage RWHS in Malaysia

6.1. Subsidies

It is noticed that rainwater harvesting scheme is less attractive in many developing countries. This is because of the high installation and maintenance cost, as well as low water tariff, which result in a long payback period. On the other hand, the success of RWHS in developed countries is contributed to by the support from the government, especially during the initial stages of implementation.
Several countries have introduced subsidies for the premise owner who installed RWHS. For instance in Spain, there are subsidies of up to €1200 for each house owner who has installed RWHS on their own initiative [65]. Australian government has also launched the Home Water Wise Rebate scheme, which provides subsidies to residents who have implemented RWHS for non-potable domestics uses [131]. In Germany, the government supported the installation of RWHS in new or existing households by subsidizing 1/3 of the total costs or up to €2000 [132]. Other countries such as Japan, Uganda, USA, and Germany have also paid attention to encourage RWHS implementation by providing subsidy and low interest, subsidy for construction materials, rebates and tax exemptions, and exemptions from stormwater taxes, respectively. Therefore, similar subsidy scheme can be adopted to boost the implementation of RWHS in Malaysia.

6.2. Regulate Piped Water Use

Another instrument that could be adopted by the Malaysian government to encourage RWHS is by restricting the use of piped water, especially during critical periods. Such measure has been implemented in Australia by restricting the use of water for non-essential purposes such as watering lawns and washing cars at individual premises for certain states particularly during drought seasons [133]. In Singapore, an additional fee of 3.69 S$/m3, which is increased more than the normal tariff (2.74 S$/m3), is collected when the amount of water used exceeds 40 m3 [134]. Similarly, the local water and sewage utility in Brazil imposes a much higher tariff (5.66 R$/m3) when the consumption is higher than 10 m3/month compared to the normal rate (3.43 R$/m3) [135].
Malaysia could emulate such strategy by first educating the public using formal and informal platforms, especially among school children. This should be strengthened by regulations and guidelines. The benefit could be highlighted by providing appropriate tools such as rainwater harvesting software, which includes system design and economic assessment. Moreover, the present water tariff structures in Malaysia seem to be less effective at encouraging the public to save water. A higher water tariff that could change water use behavior might be necessary. Alternatively, more stringent regulation could be introduced for non-essential purposes, particularly for states that experience long dry period and have limited water resources.

7. Conclusions

This paper evaluated the progress of rainwater harvesting implementation globally with a focus on making possible improvements in Malaysia. The implementation of RWHS in Malaysia is very timely because of several water issues such as increasing water demand, high rainfall, and over-dependent on surface water. It is proven that RWHS could offer various socio-economic and environmental benefits. The benefits are bill saving, flash flood reduction, and delaying the need for constructing new water supply infrastructure. Malaysian government has long implemented RWHS, especially in government and public buildings. However, overall the success is still inadequate mainly due to the relatively high investment, low water tariff, lack of incentive from the authorities, low public awareness, and poor enforcement. RWHS is more profitable when implemented on a large scale such as in commercial buildings compared to small scale systems in a residential area. This is because of the large roof area that provides enough volume for high consumption in addition to a higher water tariff compared to a domestic tariff. Several improvements on policy implementation are necessary in order to gain wider acceptance of RWHS, which includes providing an appropriate incentive and regulating the excessive use of piped water.

Acknowledgments

The authors thank the Malaysian Ministry of Science, Technology, and Innovation (MOSTI) for financial supporting under the Science Fund scheme (R.J130000.7909.4S137) and the Universiti Teknologi Malaysia for facilitating the research work. Collaboration and support from AEON CO. (M) Bhd are highly appreciated.

Author Contributions

N.H.L. collected the relevant data and contributed to the drafting of the manuscript. Z.Y. and A.S. directed the project and contributed critical discussion. All authors reviewed and approved the manuscript.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Vörösmarty, C.J.; Green, P.; Salisbury, J.; Lammers, R.B. Global water resources: Vulnerability from climate change and population growth. Science 2000, 289, 284–288. [Google Scholar] [CrossRef] [PubMed]
  2. Ercin, A.E.; Hoekstra, A.Y. Water footprint scenarios for 2050: A global analysis. Environ. Int. 2014, 64, 71–82. [Google Scholar] [CrossRef] [PubMed]
  3. De Fraiture, C.; Wichelns, D. Satisfying future water demands for agriculture. Agric. Water Manag. 2010, 97, 502–511. [Google Scholar] [CrossRef]
  4. Oki, T.; Agata, Y.; Kanae, S.; Saruhashi, T.; Yang, D.; Musiake, K. Global assessment of current water resources using total runoff integrating pathways. Hydrol. Sci. J. 2001, 46, 983–995. [Google Scholar] [CrossRef]
  5. Wolfe, S.; Brooks, D.B. Water scarcity: An alternative view and its implications for policy and capacity building. Nat. Resour. Forum 2003, 27, 99–107. [Google Scholar] [CrossRef]
  6. Rijsberman, F.R. Water scarcity: Fact or fiction? Agric. Water Manag. 2006, 80, 5–22. [Google Scholar] [CrossRef]
  7. Matos, C.; Santos, C.; Pereira, S.; Bentes, I.; Imteaz, M. Rainwater storage tank sizing: Case study of a commercial building. Int. J. Sustain. Built. Env. 2013, 2, 109–118. [Google Scholar] [CrossRef]
  8. Abdulla, F.A.; Al-Shareef, A.W. Roof rainwater harvesting systems for household water supply in Jordan. Desalination 2009, 243, 195–207. [Google Scholar] [CrossRef]
  9. Helmreich, B.; Horn, H. Opportunities in rainwater harvesting. Desalination 2009, 248, 118–124. [Google Scholar] [CrossRef]
  10. Belmeziti, A.; Coutard, O.; de Gouvello, B. How much drinking water can be saved by using rainwater harvesting on a large urban area? Application to Paris agglomeration. Water Sci. Technol. 2014, 70, 1782–1788. [Google Scholar] [CrossRef] [PubMed]
  11. Vieira, A.S.; Beal, C.D.; Ghisi, E.; Stewart, R.A. Energy intensity of rainwater harvesting systems: A review. Renew. Sust. Energ. Rev. 2014, 34, 225–242. [Google Scholar] [CrossRef]
  12. Fonseca, C.R.; Hidalgo, V.; Díaz-Delgado, C.; Vilchis-Francés, A.Y.; Gallego, I. Design of optimal tank size for rainwater harvesting systems through use of a web application and geo-referenced rainfall patterns. J. Clean. Prod. 2017, 145, 323–335. [Google Scholar] [CrossRef]
  13. Sample, D.J.; Liu, J. Optimizing rainwater harvesting systems for the dual purposes of water supply and runoff capture. J. Clean. Prod. 2014, 75, 174–194. [Google Scholar] [CrossRef]
  14. Morales-Pinzón, T.; Rieradevall, J.; Gasol, C.M.; Gabarrell, X. Modelling for economic cost and environmental analysis of rainwater harvesting systems. J. Clean. Prod. 2015, 87, 613–626. [Google Scholar] [CrossRef]
  15. Palla, A.; Gnecco, I.; La Barbera, P. The impact of domestic rainwater harvesting systems in storm water runoff mitigation at the urban block scale. J. Environ. Manag. 2017, 191, 297–305. [Google Scholar] [CrossRef] [PubMed]
  16. de Gois, E.H.; Rios, C.A.; Costanzi, R.N. Evaluation of water conservation and reuse: A case study of a shopping mall in southern Brazil. J. Clean. Prod. 2015, 96, 263–271. [Google Scholar] [CrossRef]
  17. Tam, V.W.Y.; Tam, L.; Zeng, S.X. Cost effectiveness and tradeoff on the use of rainwater tank: An empirical study in Australian residential decision-making. Resour. Conserv. Recycl. 2010, 54, 178–186. [Google Scholar] [CrossRef]
  18. Farreny, R.; Gabarrell, X.; Rieradevall, J. Cost-efficiency of rainwater harvesting strategies in dense Mediterranean neighbourhoods. Resour. Conserv. Recycl. 2011, 55, 686–694. [Google Scholar] [CrossRef]
  19. Kim, K.; Yoo, C. Hydrological modeling and evaluation of rainwater harvesting facilities: Case study on several rainwater harvesting facilities in korea. J. Hydrol. Eng. 2009, 14, 545–561. [Google Scholar] [CrossRef]
  20. Fewkes, A. A review of rainwater harvesting in the UK. Struct. Surv. 2012, 30, 174–194. [Google Scholar] [CrossRef]
  21. Coombes, P.J.; Kuczera, G.; Kalma, J.D.; Argue, J.R. An evaluation of the benefits of source control measures at the regional scale. Urban Water 2002, 4, 307–320. [Google Scholar] [CrossRef]
  22. Farahbakhsh, K.; Despins, C.; Leidl, C. Developing capacity for large-scale rainwater harvesting in Canada. Water Qual. Res. J. Can. 2009, 44, 92–102. [Google Scholar]
  23. Baguma, D.; Loiskandl, W.; Jung, H. Water management, rainwater harvesting and predictive variables in rural households. Water Resour. Manag. 2010, 24, 3333–3348. [Google Scholar] [CrossRef]
  24. Abdulla, F.A.; Al-shareef, A.W. Assessment of Rainwater Roof Harvesting Systems for Household Water Supply in Jordan. In Integrated Urban Water Resources Management; Springer: Berlin, Germany, 2006; pp. 291–300. [Google Scholar]
  25. Coombes, P.J. Energy and economic impacts of rainwater tanks on the operation of regional water systems. Australas. J. Water Res. 2007, 11, 177–191. [Google Scholar] [CrossRef]
  26. Cole, G.; Stewart, R.A. Smart meter enabled disaggregation of urban peak water demand: Precursor to effective urban water planning. Urban Water J. 2013, 10, 174–194. [Google Scholar] [CrossRef]
  27. Lucas, S.; Coombes, P.; Sharma, A. The impact of diurnal water use patterns, demand management and rainwater tanks on water supply network design. Water Sci. Technol. 2010, 10, 69–80. [Google Scholar] [CrossRef]
  28. Gurung, T.R.; Stewart, R.A.; Beal, C.D.; Sharma, A.K. Investigating the financial implications and viability of diversified water supply systems in an urban water supply zone. Water Resour. Manag. 2016, 30, 4037–4051. [Google Scholar] [CrossRef]
  29. Carragher, B.J.; Stewart, R.A.; Beal, C.D. Quantifying the influence of residential water appliance efficiency on average day diurnal demand patterns at an end use level: A precursor to optimised water service infrastructure planning. Resour. Conserv. Recycl. 2012, 62, 81–90. [Google Scholar] [CrossRef]
  30. Aladenola, O.O.; Adeboye, O.B. Assessing the potential for rainwater harvesting. Water Resour. Manag. 2010, 24, 2129–2137. [Google Scholar] [CrossRef]
  31. Jones, M.P.; Hunt, W.F. Performance of rainwater harvesting systems in the southeastern United States. Resour. Conserv. Recycl. 2010, 54, 623–629. [Google Scholar] [CrossRef]
  32. Vaes, G.; Berlamont, J. The effect of rainwater storage tanks on design storms. Urban Water 2001, 3, 303–307. [Google Scholar] [CrossRef]
  33. Shaaban, A.; Appan, A. Utilising rainwater for non-potable domestic uses and reducing peak urban runoff in Malaysia. In Proceedings of the 11th International Rainwater Catchment Systems Conference, Mexico City, Mexico, 25–29 August 2003. [Google Scholar]
  34. Parece, T.E.; Lumpkin, M.; Campbell, J.B. Irrigating urban agriculture with harvested rainwater: Case study in Roanoke, Virginia, USA. In Sustainable Water Management in Urban Environments; Younos, T., Parece, T.E., Eds.; Springer International Publishing: Cham, Switzerland, 2016; pp. 235–263. [Google Scholar]
  35. Motsi, K.E.; Chuma, E.; Mukamuri, B.B. Rainwater harvesting for sustainable agriculture in communal lands of Zimbabwe. Phys. Chem. Earth 2004, 29, 1069–1073. [Google Scholar] [CrossRef]
  36. Bruins, H.J.; Evenari, M.; Nessler, U. Rainwater-harvesting agriculture for food production in arid zones: The challenge of the African famine. Appl. Geogr. 1986, 6, 13–32. [Google Scholar] [CrossRef]
  37. Bocanegra-Martínez, A.; Ponce-Ortega, J.M.; Nápoles-Rivera, F.; Serna-González, M.; Castro-Montoya, A.J.; El-Halwagi, M.M. Optimal design of rainwater collecting systems for domestic use into a residential development. Resour. Conserv. Recycl. 2014, 84, 44–56. [Google Scholar] [CrossRef]
  38. Fisher-Jeffes, L.; Armitage, N.; Carden, K. The viability of domestic rainwater harvesting in the residential areas of the Liesbeek River Catchment, Cape Town. Water SA 2017, 43, 81–90. [Google Scholar] [CrossRef]
  39. Silva, A.S.; Ghisi, E. Uncertainty analysis of daily potable water demand on the performance evaluation of rainwater harvesting systems in residential buildings. J. Environ. Manag. 2016, 180, 82–93. [Google Scholar] [CrossRef] [PubMed]
  40. Kim, H.W.; Li, M.-H.; Kim, H.; Lee, H.K. Cost-benefit analysis and equitable cost allocation for a residential rainwater harvesting system in the city of Austin, Texas. Int. J. Water. Resour. D 2016, 32, 749–764. [Google Scholar] [CrossRef]
  41. Lopes, A.C.; Rupp, R.F.; Ghisi, E. Assessment of the potential for potable water savings by using rainwater in houses in southern Brazil. Water Sci. Technol. 2016, 16, 533–541. [Google Scholar] [CrossRef]
  42. Notaro, V.; Liuzzo, L.; Freni, G. Reliability analysis of rainwater harvesting systems in southern Italy. Procedia Eng. 2016, 162, 373–380. [Google Scholar] [CrossRef]
  43. Angrill, S.; Segura-Castillo, L.; Petit-Boix, A.; Rieradevall, J.; Gabarrell, X.; Josa, A. Environmental performance of rainwater harvesting strategies in Mediterranean buildings. Int. J. Life Cycle Assess. 2017, 22, 398–409. [Google Scholar] [CrossRef]
  44. Sountharajah, D.P.; Kus, B.; Kandasamy, J.; Vigneswaran, S. Quantifying the reduction in water demand due to rainwater tank installations at residential properties in sydney. J. Sustain. Dev. Energy Water Environ. Syst. 2017, 5, 202–218. [Google Scholar] [CrossRef]
  45. Sly, D.; Stec, A. The analysis of variants of water supply systems in multi-family residential building. Ecol. Chem. Eng. 2015, 21, 623–635. [Google Scholar]
  46. Karim, M.R.; Bashar, M.Z.I.; Imteaz, M.A. Reliability and economic analysis of urban rainwater harvesting in a megacity in Bangladesh. Resour. Conserv. Recycl. 2015, 104, 61–67. [Google Scholar] [CrossRef]
  47. Liuzzo, L.; Notaro, V.; Freni, G. A reliability analysis of a rainfall harvesting system in Southern Italy. Water 2016, 8, 18. [Google Scholar] [CrossRef]
  48. Taffere, G.R.; Beyene, A.; Vuai, S.A.H.; Gasana, J.; Seleshi, Y. Characterization of atmospheric bulk deposition: Implications on the quality of rainwater harvesting systems in the semi-arid city of Mekelle, Northern Ethiopia. Environ. Process. 2016, 3, 247–261. [Google Scholar] [CrossRef]
  49. Chilton, J.C.; Maidment, G.G.; Marriott, D.; Francis, A.; Tobias, G. Case study of a rainwater recovery system in a commercial building with a large roof. Urban Water 2000, 1, 345–354. [Google Scholar] [CrossRef]
  50. Ward, S.; Memon, F.A.; Butler, D. Performance of a large building rainwater harvesting system. Water Res. 2012, 46, 5127–5134. [Google Scholar] [CrossRef] [PubMed]
  51. Cook, S.; Sharma, A.K.; Gurung, T.R. Evaluation of alternative water sources for commercial buildings: A case study in Brisbane, Australia. Resour. Conserv. Recycl. 2014, 89, 86–93. [Google Scholar] [CrossRef]
  52. Rahman, A.; Keane, J.; Imteaz, M.A. Rainwater harvesting in Greater Sydney: Water savings, reliability and economic benefits. Resour. Conserv. Recycl. 2012, 61, 16–21. [Google Scholar] [CrossRef]
  53. Basinger, M.; Montalto, F.; Lall, U. A rainwater harvesting system reliability model based on nonparametric stochastic rainfall generator. J. Hydrol. 2010, 392, 105–118. [Google Scholar] [CrossRef]
  54. Rashidi Mehrabadi, M.H.; Saghafian, B.; Haghighi Fashi, F. Assessment of residential rainwater harvesting efficiency for meeting non-potable water demands in three climate conditions. Resour. Conserv. Recycl. 2013, 73, 86–93. [Google Scholar] [CrossRef]
  55. Hashim, H.; Hudzori, A.; Yusop, Z.; Ho, W.S. Simulation based programming for optimization of large-scale rainwater harvesting system: Malaysia case study. Resour. Conserv. Recycl. 2013, 80, 1–9. [Google Scholar] [CrossRef]
  56. Hudzori, A.B. Optimization model of large scale rainwater harvesting system. In Chemical Engineering; Universiti Teknologi Malaysia: Skudai, Malaysia, 2017. [Google Scholar]
  57. Chiu, Y.-R.; Liaw, C.-H.; Chen, L.-C. Optimizing rainwater harvesting systems as an innovative approach to saving energy in hilly communities. Renew. Energy 2009, 34, 492–498. [Google Scholar] [CrossRef]
  58. Campisano, A.; Gnecco, I.; Modica, C.; Palla, A. Designing domestic rainwater harvesting systems under different climatic regimes in Italy. Water Sci. Technol. 2013, 67, 2511–2518. [Google Scholar] [CrossRef] [PubMed]
  59. Ward, S.; Butler, D.; Barr, S.; Memon, F.A. A framework for supporting rainwater harvesting in the UK. Water Sci. Technol. 2009, 60, 2629–2636. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  60. Melville-Shreeve, P.; Ward, S.; Butler, D. Rainwater harvesting typologies for UK houses: A multi criteria analysis of system configurations. Water 2016, 8, 129. [Google Scholar] [CrossRef] [Green Version]
  61. Ward, S.; Barr, S.; Butler, D.; Memon, F.A. Rainwater harvesting in the UK: Socio-technical theory and practice. Technol. Forecast. Soc. Chang. 2012, 79, 1354–1361. [Google Scholar] [CrossRef]
  62. Ward, S.; Barr, S.; Memon, F.; Butler, D. Rainwater harvesting in the UK: Exploring water-user perceptions. Urban Water J. 2013, 10, 112–126. [Google Scholar] [CrossRef]
  63. Hajani, E.; Rahman, A. Reliability and cost analysis of a rainwater harvesting system in peri-urban regions of Greater Sydney, Australia. Water 2014, 6, 945–960. [Google Scholar] [CrossRef]
  64. Furumai, H.; Kim, J.; Imbe, M.; Okui, H. Recent application of rainwater storage and harvesting in Japan. In Proceedings of the the 3rd RWHM Workshop, Yosemite National Park, CA, USA, 10–13 March 2008. [Google Scholar]
  65. Domènech, L.; Saurí, D. A comparative appraisal of the use of rainwater harvesting in single and multi-family buildings of the Metropolitan Area of Barcelona (Spain): Social experience, drinking water savings and economic costs. J. Clean. Prod. 2011, 19, 598–608. [Google Scholar] [CrossRef]
  66. Herrmann, T.; Schmida, U. Rainwater utilisation in Germany: Efficiency, dimensioning, hydraulic and environmental aspects. Urban Water 2000, 1, 307–316. [Google Scholar] [CrossRef]
  67. Rahman, A.; Dbais, J.; Islam, S.M.; Eroksuz, E.; Haddad, K. Rainwater harvesting in large residential buildings in Australia. In Urban Development; Polyzos, S., Ed.; InTech: Rijeka, Croatia, 2012; pp. 159–178. [Google Scholar]
  68. Cheng, C.; Liao, M.; Lee, M. A quantitative evaluation method for rainwater use guideline. Build. Serv. Eng. Res. Technol. 2006, 27, 209–218. [Google Scholar] [CrossRef]
  69. Baguma, D.; Loiskandl, W. Rainwater harvesting technologies and practises in rural Uganda: A case study. Mitig. Adapt. Strateg. Glob. Chang 2010, 15, 355–369. [Google Scholar] [CrossRef]
  70. Abdel Khaleq, R.A.; Dziegielewski, B. A national water demand management policy in Jordan. Manag. Environ. Qual. 2006, 17, 216–225. [Google Scholar] [CrossRef]
  71. Che-Ani, A.; Shaari, N.; Sairi, A.; Zain, M.; Tahir, M. Rainwater harvesting as an alternative water supply in the future. Eur. J. Sci. Res. 2009, 34, 132–140. [Google Scholar]
  72. Kabiri, R.; Ramani Bai, V.; Chan, A. Assessment of hydrologic impacts of climate change on the runoff trend in Klang Watershed, Malaysia. Environ. Earth Sci. 2015, 73, 27–37. [Google Scholar] [CrossRef]
  73. Alam, M.; Siwar, C.; Talib, B.; Toriman, M.E.B. Impacts of climatic changes on paddy production in Malaysia: Micro study on IADA at North West Selangor. Res. J. Environ. Earth Sci. 2014, 6, 251–258. [Google Scholar]
  74. Water Efficiency. Available online: http://www.awer.org.my (accessed on 20 November 2017).
  75. Tan, M.; Ibrahim, A.; Duan, Z.; Cracknell, A.; Chaplot, V. Evaluation of six high-resolution satellite and ground-based precipitation products over Malaysia. Remote Sens. 2015, 7, 1504. [Google Scholar] [CrossRef]
  76. Singapore Water Story. Available online: https://www.pub.gov.sg (accessed on 23 March 2018).
  77. Water Statistics. Available online: http://www.span.gov.my (accessed on 1 December 2017).
  78. Rainwater Harvesting. Available online: http://www.jkt.kpkt.gov.my (accessed on 1 November 2017).
  79. New Development and Challenges in Malaysian Drinking Water Supply. Available online: http://slideplayer.com/slide/5175607/ (accessed on 25 March 2018).
  80. Freshwater. Available online: http://www.wwf.org.my (accessed on 26 March 2018).
  81. Avoiding Water Crisis in Malaysia Lessons for the Future. Available online: http://www.mwa.org.my (accessed on 26 March 2018).
  82. Silva, C.M.; Sousa, V.; Carvalho, N.V. Evaluation of rainwater harvesting in Portugal: Application to single-family residences. Resour. Conserv. Recycl. 2015, 94, 21–34. [Google Scholar] [CrossRef]
  83. Olsen, C.; Kowalewski, A.; Gould, M.; Lambrinos, J. Evaluating two rainwater harvesting systems in an urban setting in Oregon’s willamette valley. J. Green Build. 2017, 12, 1–10. [Google Scholar] [CrossRef]
  84. Stout, D.T.; Walsh, T.C.; Burian, S.J. Ecosystem services from rainwater harvesting in India. Urban Water J. 2017, 14, 561–573. [Google Scholar] [CrossRef]
  85. Almazroui, M.; Islam, M.N.; Balkhair, K.S.; Şen, Z.; Masood, A. Rainwater harvesting possibility under climate change: A basin-scale case study over western province of Saudi Arabia. Atmos. Res. 2017, 189, 11–23. [Google Scholar] [CrossRef]
  86. Campisano, A.; Butler, D.; Ward, S.; Burns, M.J.; Friedler, E.; DeBusk, K.; Fisher-Jeffes, L.N.; Ghisi, E.; Rahman, A.; Furumai, H.; et al. Urban rainwater harvesting systems: Research, implementation and future perspectives. Water Res. 2017, 115, 195–209. [Google Scholar] [CrossRef] [PubMed]
  87. Mwamila, T.B.; Han, M.Y.; Ndomba, P.M.; Katambara, Z. Performance evaluation of rainwater harvesting system and strategy for dry season challenge. Water Pract. Technol. 2016, 11, 829–837. [Google Scholar] [CrossRef]
  88. Asadieh, B.; Krakauer, N.Y. Impacts of changes in precipitation amount and distribution on water resources studied using a model rainwater harvesting system. J. Am. Water Resour. Assoc. 2016, 52, 1450–1471. [Google Scholar] [CrossRef]
  89. Assefa, S.; Biazin, B.; Muluneh, A.; Yimer, F.; Haileslassie, A. Rainwater harvesting for supplemental irrigation of onions in the southern dry lands of Ethiopia. Agric. Water Manag. 2016, 178, 325–334. [Google Scholar] [CrossRef]
  90. Haque, M.M.; Rahman, A.; Samali, B. Evaluation of climate change impacts on rainwater harvesting. J. Clean. Prod. 2016, 137, 60–69. [Google Scholar] [CrossRef]
  91. Leong, J.Y.C.; Chong, M.N.; Poh, P.E.; Hermawan, A.; Talei, A. Longitudinal assessment of rainwater quality under tropical climatic conditions in enabling effective rainwater harvesting and reuse schemes. J. Clean. Prod. 2017, 143, 64–75. [Google Scholar] [CrossRef]
  92. Scopus. Available online: https://www.scopus.com (accessed on 1 February 2018).
  93. Lee, K.E.; Mokhtar, M.; Mohd Hanafiah, M.; Abdul Halim, A.; Badusah, J. Rainwater harvesting as an alternative water resource in Malaysia: Potential, policies and development. J. Clean. Prod. 2016, 126, 218–222. [Google Scholar] [CrossRef]
  94. Implementation of Rainwater Harvesting in Malaysia. Available online: http://www.eng.warwick.ac.uk (accessed on 10 November 2017).
  95. Tesfuhuney, W.A.; Walker, S.; Van Rensburg, L.D.; Steyn, A.S. Micrometeorological measurements and vapour pressure deficit relations under in-field rainwater harvesting. Phys. Chem. Earth 2016, 94, 196–206. [Google Scholar] [CrossRef]
  96. Kasmin, H.; Bakar, N.H.; Zubir, M.M. Monitoring on the quality and quantity of DIY rainwater harvesting system. IOP Conf. Ser. Mater. Sci. Eng. 2016, 136, 1–8. [Google Scholar] [CrossRef]
  97. Abdul Ghani, N.A.A.; Mohamad, N.A.; Hui, T.W. Rainfall analysis to determine the potential of rainwater harvesting site in Kuantan, Pahang. ARPN J. Eng. Appl. Sci. 2016, 11, 7264–7268. [Google Scholar]
  98. Sultana, N.; Akib, S.; Aqeel Ashraf, M.; Roseli Zainal Abidin, M. Quality assessment of harvested rainwater from green roofs under tropical climate. Desalination Water Treat. 2016, 57, 75–82. [Google Scholar] [CrossRef]
  99. Nasif, M.S.; Roslan, R. Effect of varying roof run-off coefficient values and tank size on rainwater harvesting system’s water savings in Malaysia. ARPN J. Eng. Appl. Sci. 2016, 11, 12937–12941. [Google Scholar]
  100. Rahman, S.A.; Othman, M.S.H.; Khalid, R.M.; Shawahid, F.M. Legal implications of compulsory rainwater harvesting in Malaysia. J. Food Agric. Env. 2013, 11, 2077–2079. [Google Scholar]
  101. Shaheed, R.; Mohtar, W.H.M.W. Potential of using rainwater for potable purpose in Malaysia with varying antecedent dry intervals. Jurnal Teknologi 2015, 72, 57–61. [Google Scholar] [CrossRef]
  102. Hamid, T.A.; Nordin, B. Green campus initiative: Introducing RWH system in Kolej Perindu 3 UiTM Malaysia. In Proceedings of the 3rd International Symposium & Exhibition in Sustainable Energy & Environment, Melaka, Malaysia, 1–3 June 2011. [Google Scholar]
  103. Imteaz, M.A.; Shanableh, A.; Rahman, A.; Ahsan, A. Optimisation of rainwater tank design from large roofs: A case study in Melbourne, Australia. Resour. Conserv. Recycl. 2011, 55, 1022–1029. [Google Scholar] [CrossRef]
  104. Roebuck, R.M.; Oltean-Dumbrava, C.; Tait, S. Whole life cost performance of domestic rainwater harvesting systems in the United Kingdom. Water Environ. J. 2011, 25, 355–365. [Google Scholar] [CrossRef]
  105. Zhang, Y.; Chen, D.; Chen, L.; Ashbolt, S. Potential for rainwater use in high-rise buildings in Australian cities. J. Environ. Manag. 2009, 91, 222–226. [Google Scholar] [CrossRef] [PubMed]
  106. Ghisi, E.; Schondermark, P.N. Investment feasibility analysis of rainwater use in residences. Water Resour. Manag. 2013, 27, 2555–2576. [Google Scholar] [CrossRef]
  107. Khastagir, A.; Jayasuriya, N. Investment evaluation of rainwater tanks. Water Resour. Manag. 2011, 25, 3769–3784. [Google Scholar] [CrossRef]
  108. Matos, C.; Bentes, I.; Santos, C.; Imteaz, M.; Pereira, S. Economic analysis of a rainwater harvesting system in a commercial building. Water Resour. Manag. 2015, 29, 3971–3986. [Google Scholar] [CrossRef]
  109. Imteaz, M.A.; Moniruzzaman, M. Spatial variability of reasonable government rebates for rainwater tank installations: A case study for Sydney. Resour. Conserv. Recycl. 2018, 133, 112–119. [Google Scholar] [CrossRef]
  110. Shaari, N.; Che-Ani, A.I.; Nasir, N.; Tawil, N.M.; Jamil, M. Implementation of rainwater harvesting in Sandakan: Evolution of sustainable architecture in Malaysia. In Proceedings of the Regional Engineering Postgraduate Conference, Kuantan, Malaysia, 20–21 October 2009. [Google Scholar]
  111. Ghisi, E.; Ferreira, D.F. Potential for potable water savings by using rainwater and greywater in a multi-storey residential building in southern Brazil. Build. Environ. 2007, 42, 2512–2522. [Google Scholar] [CrossRef]
  112. Sanches Fernandes, L.F.; Terêncio, D.P.S.; Pacheco, F.A.L. Rainwater harvesting systems for low demanding applications. Sci. Total Environ. 2015, 529, 91–100. [Google Scholar] [CrossRef] [PubMed]
  113. Mwenge Kahinda, J.; Taigbenu, A.E.; Boroto, R.J. Domestic rainwater harvesting as an adaptation measure to climate change in South Africa. Phys. Chem. Earth 2010, 35, 742–751. [Google Scholar] [CrossRef]
  114. Kihila, J. Rainwater harvesting using Ferro cement tanks an appropriate and affordable technology for small rural Institutions in Tanzania. Int. J. Civ. Struct. Eng. 2014, 4, 332–341. [Google Scholar]
  115. Gathenya, J.; Kinyari, P.; Home, P. Domestic roof rainwater harvesting tank sizing calculator and nomograph. J. Agric. Sci. Technol. 2011, 12, 115–125. [Google Scholar]
  116. Khan, S.T.; Baksh, A.A.; Papon, M.T.I.; Ali, M.A. Rainwater harvesting system: An approach for optimum tank size design and assessment of efficiency. Int. J. Environ. Sci. Dev. 2017, 8, 37–43. [Google Scholar] [CrossRef]
  117. Perisian Tangki NAHRIM. Available online: https://www.nahrim.gov.my (accessed on 20 November 2017).
  118. Al-Saffar, F.N.; Abood, M.M.; Haron, N.A. Harvested rainwater volume estimation using tangki nahrim software: Calculation of the optimum tank size in terms of water security. Aust. J. Basic Appl. Sci. 2016, 10, 40–48. [Google Scholar]
  119. Holt, M.S. Sources of chemical contaminants and routes into the freshwater environment. Food Chem. Toxicol. 2000, 38, S21–S27. [Google Scholar] [CrossRef]
  120. Appan, A. Roof water collection systems in some Southeast Asian countries: Status and water quality levels. J. R. Soc. Health 1997, 117, 319–323. [Google Scholar] [CrossRef] [PubMed]
  121. Sazakli, E.; Alexopoulos, A.; Leotsinidis, M. Rainwater harvesting, quality assessment and utilization in Kefalonia Island, Greece. Water Res. 2007, 41, 2039–2047. [Google Scholar] [CrossRef] [PubMed]
  122. Kim, R.-H.; Lee, S.; Kim, J.-O. Application of a metal membrane for rainwater utilization: Filtration characteristics and membrane fouling. Desalination 2005, 177, 121–132. [Google Scholar] [CrossRef]
  123. Buntat, Z.; Iqbal, S.M.Z.; Saburi, W.M.F.A.; Adzis, Z.; Sohaili, J.; Smith, I.R. Development of an Integrated System for Ozone Treated Harvested Rainwater in Perspective of Green Building Scenario of Malaysia. J. Environ. Earth Sci. 2015, 5, 51–60. [Google Scholar]
  124. Omar, K.; Aziz, N.; Amr, S.; Palaniandy, P. Removal of lindane and Escherichia coli (E. coli) from rainwater using photocatalytic and adsorption treatment processes. Glob. Nest J. 2017, 19, 191–198. [Google Scholar]
  125. Shaheed, R.; Wan Mohtar, W.H.M.; El-Shafie, A. Ensuring water security by utilizing roof-harvested rainwater and lake water treated with a low-cost integrated adsorption-filtration system. Water Sci. Eng. 2017, 10, 115–124. [Google Scholar] [CrossRef]
  126. Möller, D.; Zierath, R. On the composition of precipitation water and its acidity. Tellus B Chem. Phys. Meteorol. 1986, 38, 44–50. [Google Scholar] [CrossRef]
  127. Nikmatin, S.; Syafiuddin, A.; Hong Kueh, A.B.; Maddu, A. Physical, thermal, and mechanical properties of polypropylene composites filled with rattan nanoparticles. J. App. Res. Technol. 2017, 15, 386–395. [Google Scholar] [CrossRef]
  128. The Aging Water Infrastructure: Out of Sight, out of Mind? Available online: https://www2.deloitte.com (accessed on 10 November 2017).
  129. Water Price Revision. Available online: https://www.pub.gov.sg (accessed on 1 February 2018).
  130. Chin, R.J.; Lai, S.H.; Chang, K.B.; Othman, F.; Jaafar, W.Z.W. Analysis of rainfall events over Peninsular Malaysia. Weather 2016, 71, 118–123. [Google Scholar] [CrossRef]
  131. Ahmed, W.; Gardner, T.; Toze, S. Microbiological quality of roof-harvested rainwater and health risks: A review. J. Environ. Qual. 2011, 40, 13–21. [Google Scholar] [CrossRef] [PubMed]
  132. Schuetze, T. Rainwater harvesting and management—Policy and regulations in Germany. Water Sci. Technol. 2013, 13, 376–385. [Google Scholar] [CrossRef]
  133. Dolnicar, S.; Hurlimann, A.; Grün, B. Water conservation behavior in Australia. J. Environ. Manag. 2012, 105, 44–52. [Google Scholar] [CrossRef] [PubMed]
  134. Dealing with Water Scarcity in Singapore: Institutions, Strategies, and Enforcement. Available online: http://www.siteresources.worldbank.org (accessed on 10 November 2017).
  135. Ghisi, E.; Tavares, D.D.F.; Rocha, V.L. Rainwater harvesting in petrol stations in Brasília: Potential for potable water savings and investment feasibility analysis. Resour. Conserv. Recycl. 2009, 54, 79–85. [Google Scholar] [CrossRef]
Figure 1. Annual rainfall intensity map over Malaysia [75].
Figure 1. Annual rainfall intensity map over Malaysia [75].
Water 10 00506 g001
Figure 2. (a) Non-revenue water, (b) domestic water consumption, and (c) water tariff for Johor, Malaysia. RM1 is equal to 0.28USD obtained from an average currency data from 01/2008 to 01/2018.
Figure 2. (a) Non-revenue water, (b) domestic water consumption, and (c) water tariff for Johor, Malaysia. RM1 is equal to 0.28USD obtained from an average currency data from 01/2008 to 01/2018.
Water 10 00506 g002
Figure 3. (a) Publications from 1966 to May 2017, (b) subject area, (c) countries publishing RWHS topic, and (d) source of title publishing RWHS topic identified via keywords “RWHS” in Scopus database accessed on 9 February 2018 [92].
Figure 3. (a) Publications from 1966 to May 2017, (b) subject area, (c) countries publishing RWHS topic, and (d) source of title publishing RWHS topic identified via keywords “RWHS” in Scopus database accessed on 9 February 2018 [92].
Water 10 00506 g003
Figure 4. Typical RWHS designs of (a) backyard system, (b) frontage system, and (c) underground system implemented in Malaysia.
Figure 4. Typical RWHS designs of (a) backyard system, (b) frontage system, and (c) underground system implemented in Malaysia.
Water 10 00506 g004
Figure 5. Typical first flush design of RWHS [78].
Figure 5. Typical first flush design of RWHS [78].
Water 10 00506 g005
Table 1. Selected strategies on the benefit of RWHS.
Table 1. Selected strategies on the benefit of RWHS.
CategoriesFindingLocationReference
EconomyRWHS in a dry and highly populated urban area is less attractive under the present low water tariff scenario but it becomes more promising with increasing tariff.Barcelona, SpainFarreny et al. [18]
Annual domestic cost saving up to $240 per year per house.Seven major cities in Australia including Gold Coast, Brisbane, Melbourne, Sydney, Adelaide, Perth, and CanberraTam et al. [17]
The benefit of RWHS for water supply alone is less economical unless other benefits such as for flood control are considered.United KingdomFewkes [20]
EnvironmentRWHS is predicted to reduce flooding by 10%.KoreaKim and Yoo [19]
Prolong the water storage to be used during dry periods.Abeokuta, Southwestern part of NigeriaAladenola and Adeboye [30]
RWHS is utilised widely in areas with poor water supplies.North of Carolina, United StatesJones and Hunt [31]
Reduce dependency on piped water and delay the development of new storage infrastructure.The Lower Hunter and Central Coast region of New South Wales, AustraliaCoombes et al. [21]
Large scale rainwater tank can reduce peak flow in sewer system.BelgiumVaes and Berlamont [32]
Meet up to 34% of domestic water use and 10% reduction in peak discharge if all houses in the residential area are installed with RWHS.MalaysiaShaaban and Appan [33]
Technology and SocialEffective control of stormwater and water conservation, as well as an alternative water resource.CanadaFarahbakhsh et al. [22]
Improve household water management in rural area and reduce water-related health risks.UgandaBaguma et al. [23]
Supplement the existing groundwater and surface water resources. RW is cleaner than the existing supply.JordanAbdulla and Al-shareef [24]
Table 2. Example of implementation of RWHS.
Table 2. Example of implementation of RWHS.
LocationApplication of RWHFindingsReference
AustraliaResidential buildingsUp to 99% reliability can be achieved by implementing RWHS for non-potable useRahman et al. [52]
AustraliaResidential buildingsRWHS can meet 96% to 99% and 69% to 99% of the water demand in wettest and driest years, respectively.Hajani and Rahman [63]
New YorkResidential buildingsRWHS can meet 7 to 95% of the water demands.Basinger et al. [53]
IranResidential buildingsRWHS reliability ranges from 1.6–58.3%, 11.9–98.9%, and 0.9–31.6% for Mediterranean (rainfall 288 mm/year), humid (rainfall 1355 mm/year), and arid climates (rainfall 150 mm/year), respectivelyRashidi Mehrabadi et al. [54]
PortugalCommercial buildingsRWHS is very reliable for pavement washing and garden irrigationMatos et al. [7]
AustraliaCommercial buildingsRWHS reliability can reach 37% of the water demandsCook et al. [51]
Table 3. Legislation and incentive to encourage the use of RWHS in the world.
Table 3. Legislation and incentive to encourage the use of RWHS in the world.
CountryLegislation and ApplicationReference
JapanSubsidy and low interest loan are provided by the government to premises for RWHS installation.Furumai et al. [64]
AustraliaThe government offers up to $500 rebates to houses that install a RWHS.Rahman et al. [67]
TaiwanA new guideline for RWHS as new water conservation alternative for domestic water use is issued for national buildings.Cheng et al. [68]
UgandaThe government provides subsidies to RWHS construction materials in rural areas.Baguma and Loiskandl [69]
JordanThe government has incorporated RWHS in the water demand management policy.Abdel Khaleq and Dziegielewski [70]
SpainThe government has made it mandatory for new buildings with a certain garden area to install RWHS.Domènech and Saurí [65]
BrazilThe government has promoted a programme that aims to install one million cisterns in semi-arid areas.Domènech and Saurí [65]
BelgiumThe government has mandated for new buildings with a roof area greater than 100 m2 to install RWHS.Domènech and Saurí [65]
USA (Texas)The government provides rebates and tax exemptions to foster rainwater use.Domènech and Saurí [65]
GermanyPremises with RWHS are exempted from stormwater taxes.Herrmann and Schmida [66]
Table 4. Mean annual rainfall and number of rain-days for selected towns [78].
Table 4. Mean annual rainfall and number of rain-days for selected towns [78].
Name of TownPeriod of RecordNumber of Rain-Day/Year
Alor Star1948–2007147
Ipoh1972–2008181
Klang1953–2008132
Kuala Lumpur1953–2008177
Seremban1959–2008141
Melaka1954–1998179
Kluang1948–2006163
Johor Bahru1948–2007158
Kota Bharu1981–2008138
Kuala Terengganu1954–2008161
Kuantan1948–2008136
Kota Kinabalu1985–2009177
Table 5. Current water tariff in Malaysia [77].
Table 5. Current water tariff in Malaysia [77].
StateDomesticNon-Domestic
Johor3.003.30
Kedah1.301.80
Kelantan1.421.80
Labuan2.002.28
Melaka1.452.05
N. Sembilan1.402.70
P. Pinang1.301.45
Pahang0.990.99
Perak1.031.40
Perlis1.101.30
Selangor2.002.28
Terengganu1.001.15
The above water tariff is presented in RM/m3.
Table 6. Policies and guidelines related to RWHS under Malaysian government [93].
Table 6. Policies and guidelines related to RWHS under Malaysian government [93].
GuidelinesDepartment/AgencyYear
Guidelines for installing a Rainwater Collection and Utilization SystemMinistry of Housing and Local Government1999
RWHS: Guidebook on Planning and DesignDepartment of Irrigation and Drainage Malaysia (DID Malaysia)2009
Guideline on Eco-Efficiency in Water Infrastructure for public Buildings in MalaysiaNational Hydraulic Research Institute of Malaysia2011
Urban Stormwater Management Manual for Malaysia, MSMA 2nd EditionDID Malaysia2012
Panduan Pelaksanaan Inisiatif Pembangunan Kejiranan Hijau—Sistem Pengumpulan dan Penggunaan Semula Air HujanFederal Town and Country Planning Department2012
Garis Panduan Perancangan Kejiranan HijauFederal Town and Country Planning Department2012
Garis Panduan Sistem Pengumpulan dan Penggunaan Air HujanFederal Town and Country Planning Department, Ministry of Urban Wellbeing, Housing and Local Government2013
Urban Stormwater Management—Part 6: RWHS, MS2526-6:2014Department of Standards Malaysia2014
Table 7. Selected RWHS implemented by DID Malaysia [94].
Table 7. Selected RWHS implemented by DID Malaysia [94].
LocationTank CategoryCost (RM)
DID Office, HQ KLUnderground Tank200,000
DID District Office, Bera, PahangUnderground Pipe Package48,000
DID District Office, Raub, PahangUnderground Pipe Package185,000
DID District Office, Balik Pulau, P. PinangUnderground Pipe Package48,000
DID District Office, Seberang Perai, P. PinangUnderground Tank180,000
DID District Office, Langkawi, KedahAbove ground HDPE Tank200,000
DID District Office, Pasir Putih, KelantanAbove ground HDPE Tank200,000
DID District Office, Kuala Berang, Tere ngganuAbove ground HDPE Tank200,000
DID District Office, Miri, SarawakUnderground Pipe Package145,000
DID Mechanical Office, Ipoh, PerakAbove ground HDPE Tank200,000
University Tun Hussein Onn HostelUnderground Tank350,000
MARDI Office, Cameron Highlands, PahangAbove ground HDPE Tank40,000
State Mosque, P. PinangUnderground Tank125,000
Bukit Indah Mosque, Ampang, SelangorUnderground Tank200,000
Building Complex, Tioman, PahangAbove ground HDPE Tank200,000
Buffalo Park, Langkawi, KedahAbove ground HDPE Tank100,000
Bungalow House, Bangi, SelangorUnderground Pipe Package20,000
Terrace House, Gombak, SelangorAbove ground HDPE Tank20,000
National Zoo, Ampang, SelangorAbove ground Concrete Tank & Underground HDPE Tank400,000
Table 8. Total publication identified via keywords “rainwater harvesting” in Malaysia [92].
Table 8. Total publication identified via keywords “rainwater harvesting” in Malaysia [92].
YearNumber of Scientific Paper
20183
201710
201610
20157
20141
20136
20123
20113
20093
19891
Table 9. Top five institutions publishing RWHS topic [92].
Table 9. Top five institutions publishing RWHS topic [92].
InstitutionNumber of Scientific Paper
Universiti Kebangsaan Malaysia12
Universiti Putra Malaysia10
University of Malaya7
Universiti Teknologi MARA5
Universiti Teknologi Malaysia5
Table 10. The economic feasibility of RWHS.
Table 10. The economic feasibility of RWHS.
Location (Average Rain, mm/Year)Approach of the Researchr (%)t (Years)FindingReference
Melbourne (650)Water balance model for the performance
analysis and design
of rainwater tanks
-15 to 21The construction cost can be recovered within 15 to 21 years depending on the considered variables.Imteaz et al. [103]
West Yorkshire, UK (∼700)Life cycle costs analysis (LCCA) of RWH3.5 to 15-The domestic RWHS generally resulted in financial losses
approximately equal to their capital costs.
Roebuck et al. [104]
7 cities in Australia (520 to 1597)Costs of RWH compared to other water supply alternatives36Implementation of RWHS is an economical option for households compared to others.Tam et al. [17]
4 cities in Australia (800 to 1600)Feasibility of RWH in high-rise buildings (payback period)6.58 to 23City having the highest rainfall provides the shortest payback period in implementing RWHS.Zhang et al. [105]
Five towns in Brazil (1483 to 2002)Investment feasibility analysis of RWHS-1 to 30The higher rainwater demand provides more economic feasibility.Ghisi and Schondermark [106]
Three towns in Melbourne (454 to 1054)Investment evaluation of RWHS5 to 1030 to 46Payback period is comparatively low for a large tank.Khastagir and Jayasuriya [107]
A commercial building in PortugalEconomic Assessment of the RWH5 and 102 to 6The lower discount rate offers the reduction of the payback periods.Matos et al. [108]
Sydney metropolitan area (675 to 1160) 2.48 to 90Payback periods from 20 to 90 years can be achieved without government rebate. However, the payback periods can be brought down to 8 years when a government rebate is implemented.Imteaz and Moniruzzaman [109]
r = discount rate and t = payback period.
Table 11. Summary of roof rainwater quality for different roof types in Malaysia.
Table 11. Summary of roof rainwater quality for different roof types in Malaysia.
ParameterGalvanized Iron RoofConcrete RoofWHO Standardization
pH6.6 to 6.46.8 to 6.96.5 to 8.5
Turbidity (NTU)10 to 2225 to 255
Total solids (mg/L)64 to 119116 to 204-
Suspended solid (mg/L)52 to 9195 to 153-
Dissolved solid (mg/L)13 to 2823 to 47-
Zinc (mg/L)2.94 to 4.970.05 to 1.935
Lead (mg/L)1.45 to 2.541.02 to 2.710.05
Fecal coliforms (MPN/100 Ml)0 to 80 to 130
Total coliforms (MPN/100 mL)25 to 6341 to 750

Share and Cite

MDPI and ACS Style

Hafizi Md Lani, N.; Yusop, Z.; Syafiuddin, A. A Review of Rainwater Harvesting in Malaysia: Prospects and Challenges. Water 2018, 10, 506. https://doi.org/10.3390/w10040506

AMA Style

Hafizi Md Lani N, Yusop Z, Syafiuddin A. A Review of Rainwater Harvesting in Malaysia: Prospects and Challenges. Water. 2018; 10(4):506. https://doi.org/10.3390/w10040506

Chicago/Turabian Style

Hafizi Md Lani, Nor, Zulkifli Yusop, and Achmad Syafiuddin. 2018. "A Review of Rainwater Harvesting in Malaysia: Prospects and Challenges" Water 10, no. 4: 506. https://doi.org/10.3390/w10040506

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop