Rainwater Harvesting for Well Recharge and Agricultural Irrigation: An Adaptation Strategy to Climate Change in Central Chile

Abstract

Water scarcity in Chile, particularly in the Mediterranean region, has been exacerbated by prolonged drought and climate change. Rainwater harvesting systems (RHS) have emerged as viable solutions for addressing water shortages, particularly for agricultural irrigation and aquifer recharge. This study evaluated the implementation and efficiency of RHS in rural areas of the Biobío Region, Chile, through the design and construction of two pilot systems in Arauco and Florida. These systems were assessed based on their water collection capacity, storage efficiency, and monitoring of water level variations in wells after rainwater incorporation, using depth probes to quantify stored volumes. The hydrological design incorporated site-specific precipitation analyses, runoff coefficients, and catchment area dimensions, estimating annual precipitation of 861 mm/year for Arauco and 611 mm/year for Florida. The RHS Arauco collected and stored 40 m³ of rainwater in a flexible tank, while RHS Florida stored 10 m³ in a polyethylene tank, demonstrating the effectiveness of the system. Additionally, we analyzed the economic feasibility and quality of harvested rainwater, ensuring its suitability for agricultural use according to Chilean regulations. The cost-effectiveness analysis indicated that the cost of stored water was $263.51 USD/m³ for Arauco and $841.07 USD/m³ for Florida, highlighting larger systems are more cost-effective owing to economies of scale. The Net Present Value (NPV) was calculated using a discount rate of 6% and a useful life of 10 years, yielding CLP $9,564,745 ($10,812.7 USD) for the Florida and CLP $2,216,616 ($2505.8 USD) for the Arauco site. The results indicate that both projects are financially viable and highly profitable, offering rapid payback periods and sustainable long-term benefits. RHS significantly contributes to water availability during the dry season, reducing dependence on conventional water sources and enhancing agricultural sustainability. Based on the evaluation of the cost–benefit, water availability, and infrastructure adaptability, we infer the feasibility of large-scale implementation at locations with similar characteristics. These findings support the role of RHS in sustainable water resource management and strengthening rural resilience to climate variability, highlighting their potential as an adaptation strategy to climate change in water-scarce Mediterranean regions.

1. Introduction

Since early history, humanity has needed water for subsistence and has built systems to capture and store water. In this sense, evidence has been found of rainwater harvesting systems that date back more than 4000 years. These works have played a key role in agricultural production and in satisfying domestic needs, mainly in arid or semi-arid regions [1,2]. Rainwater harvesting systems (RHS) are structures designed to capture, filter, and store rainwater [3]. These systems have the potential to be utilized in urban areas for various purposes, such as irrigating green spaces, cleaning streets, houses, and vehicles, filling swimming pools, and serving as an alternative water source for domestic use [4]. In rural regions, RHS can increase water availability for crop irrigation [5,6]. This is particularly relevant considering that agricultural activities account for 82% of water consumption in Chile [7], with surface water being the primary water source and groundwater being used to supplement when surface water is insufficient [8]. However, this practice is not sustainable in the long term, and in arid zones, it contributes to the depletion of aquifers [8,9]. In this context, RHS can be employed as an innovative solution for the restoration and recovery of aquifers through artificial recharge techniques [4,10,11]. Their contribution primarily lies in their ability to recharge aquifers and stabilize or raise groundwater levels through the controlled infiltration of stored water [12,13]. Additionally, they help reduce pressure on conventional water sources by providing an alternative supply of water, thereby decreasing reliance on potable water and ensuring efficient utilization through rainwater storage [14]. These characteristics position RHS as an effective alternative for sustainable water resource management in rural contexts experiencing water stress, significantly contributing to the mitigation of the effects of water scarcity [15,16,17].

Water scarcity in Chile, particularly in the Mediterranean region, has become an increasingly critical issue owing to the sustained decline in precipitation and reduced water availability, both of which are intensified by climate change. Over the past 10 to 12 years, persistent megadrought has severely impacted human consumption, productive activities, and the environment [18,19,20,21]. This situation has been further exacerbated by broader climate change dynamics observed in central Chile, which have affected water availability for multiple sectors, including agriculture and hydrological resources [22,23,24]. This prolonged reduction in the surface water supply has led to a growing reliance on groundwater resources to meet both agricultural and human needs [8,25,26,27]; however, the overexploitation of aquifers has resulted in significant depletion, further exacerbating water scarcity. In response to this crisis, new applications of rainwater harvesting systems (RHS) have begun to emerge, including their use in wildfire mitigation, urban rainwater capture [28,29], and artificial aquifer recharge. Similar applications of RHS have been implemented in other regions with a Mediterranean climate. For instance, Monteiro et al. [30] investigated the integration of rainwater harvesting systems with extensive green roofs in such climates, focusing on runoff management, plant growth, and water quality, to enhance urban resilience against water stress. Kakoulas et al. [31] assessed the effectiveness of a rainwater harvesting system for non-potable domestic use on the Mediterranean island of Chios, Greece, within the context of water scarcity and climate crisis. Aquifer recharge, whether natural or artificial, is a crucial process within the hydrological cycle that plays a fundamental role in sustaining the groundwater reserves [32]. In particular, artificial recharge seeks to enhance and accelerate this process, offering a viable method to counteract declining groundwater levels. As Islam and Talukdar [33] highlighted, rainwater harvesting for artificial aquifer recharge has recently gained recognition as a promising strategy because it provides water of relatively good quality and a known volume. Recent research has demonstrated the feasibility of the rooftop rainwater harvesting system (RHS) for aquifer recharge across diverse climatic and geographical settings. Naik et al. [34] introduced a design for rooftop rainwater harvesting within a complex of 16 buildings in India, which aims to recharge aquifers by drilling multiple wells within a recharge chamber. Similarly, in the Wadi Watier region of Egypt, Fathy et al. [35] documented the utilization of dams for both storage and artificial aquifer recharge through deep wells, where harvested rainwater is directed into wells specifically designed for injection and aquifer replenishment. These studies underscore the significance of RHS as a viable strategy for sustainable groundwater management in regions experiencing water stress and climate change.

Despite the growing interest in RHS, their implementation in central Chile remains limited, with few documented cases and an underdeveloped technological framework [36]. The agricultural sector, which depends heavily on reliable water sources, has faced increasing challenges as rising temperatures and greater water demand intensify irrigation shortages [37,38]. Therefore, it is crucial to explore alternative water management strategies that can enhance resilience to climate change. Although various alternative strategies exist for water conservation and climate change adaptation (e.g., drip irrigation, desalination, water reuse, and demand management), RHS offers advantages in rural contexts because of its relatively low implementation costs, ease of integration with existing agricultural infrastructure, and minimal operational energy requirements [39,40,41]. Additionally, RHS can simultaneously enhance water availability and potentially recharge aquifers, offering combined benefits that many alternative approaches do not provide [42]. RHS have significant potential to increase water availability during dry periods; however, the lack of studies evaluating their effectiveness for aquifer recharge and agricultural irrigation has hindered their widespread adoption. There is a pressing need for further research to assess their feasibility, optimize their implementation, and demonstrate its benefits on a local scale. If proven effective, RHS systems could enhance water security in agriculture by providing a supplementary water source during dry periods, thereby extending the sustainability of regional water resources and fostering long-term resilience to climate variability. The objective of this study was to evaluate the implementation and efficiency of RHS for their potential use in well recharge and agricultural irrigation in rural areas of the Biobío Region, Chile. This study analyzed the capacity for water collection and storage in different tanks, as well as an economic analysis of their implementation and the quality of harvested water. To achieve this, two pilot RHS systems were designed and constructed in the municipalities of Arauco and Florida, considering the annual precipitation and hydrological characteristics of each site. The selected pilot sites, located in the Biobío region, were chosen based on their representativeness of the water scarcity conditions observed in other Mediterranean zones of Chile. These areas experience seasonal water deficits and rely on a combination of surface and groundwater sources, making them ideal candidates for assessing the feasibility of implementing RHS. The inclusion of two sites with distinct characteristics allowed for a comparative analysis of RHS performance under different geographical and hydrological conditions. Although these findings are specific to the site, they offer insights that could be applicable to other Mediterranean regions in Chile experiencing similar hydroclimatic challenges, thereby contributing to the development of more comprehensive water-management strategies. In light of these considerations, the question arises: To what extent does the implementation of RHS constitute a viable solution for addressing water scarcity through potential well recharge and agricultural irrigation in Biobío’s Mediterranean region? It was hypothesized that, considering the precipitation patterns and hydrological conditions of the study area, the implemented RHS would facilitate effective water accumulation, which could subsequently be used for irrigation or aquifer recharge.

Through this research, we aim to contribute to a better understanding of the implementation of an optimized RHS design that can be replicated in different Mediterranean zones to increase water availability for small-scale family farming and mitigate the effects of water scarcity in the context of climate change.

2. Materials and Methods

2.1. Study Area

The Biobío Region, located in central Chile (37°15′ S, 72°30′ W), is divided into six agro-climatic zones: Coastal Dryland, Interior Dryland, Intermediate Depression, Island Range, Foothills, and Andes Mountains [43]. The RHS Arauco and RHS Florida are situated in the rural areas of the Coastal Dryland zone of the region and are predominantly characterized by a temperate Mediterranean climate (Csb). RHS Arauco is located in the Csb(i) zone, which exhibits a more pronounced coastal influence compared to RHS Florida (Csb) (Figure 1) [44]. The Mediterranean climate in the region is characterized by dry summers and rainy winters, with a five-month dry season (November–March) and a wet season of approximately four months (May–August), during which more than 55% of the annual precipitation occurs [45]. The average annual precipitation is 1891 mm. The temperature in the warmest month is approximately 25 °C, while in the coldest month it ranges from 0 °C to 7 °C, with an annual mean temperature of 10 °C. Most of the region is covered by forests, followed by croplands, and grasslands [46]. According to the 2017 Census, the Biobío Region has a rural population of 177,790 inhabitants, representing 11.4% of the region’s total population [47]. The implementation of the RHS systems was carried out between the years 2022–2023, within the framework of the BIP 40036142-0 project of the FIC Biobío.

2.2. Hydrological Design

The pilot sites were selected based on their hydrological and climatic representativeness within the Mediterranean climate of central Chile. Arauco and Florida were chosen because of their differing topographical and land-use characteristics, allowing for a comparative evaluation of the RHS performance under distinct conditions. These differences influence key hydrological variables, such as rainfall-capture efficiency, aquifer-recharge potential, and overall system viability. Additionally, the sites were selected based on their security and accessibility, ensuring the availability of electricity and safe conditions for the construction, maintenance, and long-term monitoring of RHS systems. Given these characteristics, the evaluated RHS exhibited primary differences in their catchment structures. The RHS in Arauco employed a hillside system design incorporating a geomembrane, whereas the RHS in Florida utilized a house roof with water distribution channels. The selection of construction materials and techniques was based on the hydrological characteristics of each site to optimize the cost–benefit ratios and ensure efficient water storage.

RHS are made up of three fundamental parts [48,49]: (I) The catchment area is a waterproofed area installed on a hillside or roofs. (II) The conduction system, transport the captured water and (III) The accumulation tank, which is where rainwater is accumulated (Figure 2). Both systems were monitored over a three-month period to analyze their capacity for water collection, storage, and potential for aquifer recharge. Although the analysis is site-specific, the findings provide insights applicable to other regions experiencing similar hydroclimatic constraints.

The initial step consisted of identifying the design rainfall from which the dimensions of the RHS were estimated. Design rainfall is a key component of the hydrological design of an RHS system, and represents a calculated value that reflects the amount of rainfall expected in a specific region over a defined period. For this purpose, it was necessary to select representative rainfall stations in the study area. It is desirable for these stations to have a continuous record of at least 15 years and ideally, a record equal to or greater than the normal precipitation period (1991–2020), as this provides greater reliability in the statistical analysis and enhances the design of the RHS.

To do this, the most representative station of the area was identified at each selected site, and annual cumulative precipitation was tabulated and analyzed by frequency analysis. This allowed the annual precipitation of the station to be associated with a probability of occurrence. The Gumbel distribution is predominantly utilized for hydrological data analysis in Chile and has exhibited satisfactory fitting performance for precipitation data across various temporal scales [29,48,50,51]. However, four cumulative distribution functions (CDFs) were fitted to evaluate the best performance.

(i) CDFs tested: The Gumbel, Log-normal, Generalized Extreme Value (GEV), and Log-Pearson III distributions were fitted (

Table 1. Cumulative Distribution Functions (CDFs) fitted.

CDF	Formula
Gumbel [53]	$F\left(x\right)=e^{-e^{{\displaystyle \frac{-\left(x-\beta \right)}{\alpha }}}}$
Log-Normal [54]	$F\left(x\right)={\displaystyle \frac{1}{x\sqrt{2\pi {\sigma }^2}}}{e}^{{\displaystyle \frac{{-\left(ln\left(x\right)-\mu \right)}^2}{\sqrt{2\pi {\sigma }^2}}}}$
GEV [53]	$F\left(x\right)=e^{-{\left(1-{\displaystyle \frac{k\left(x-\mu \right)}{\alpha }}\right)}^{{\displaystyle \frac{1}{k}}}}$
Log-Pearson III [53]	$F\left(x\right)={\displaystyle \frac{({\lambda }^{\beta }{\left(\ln \left(x\right)-\epsilon \right)}^{\beta -1}{e}^{-\left(\ln \left(x\right)-\epsilon \right)}}{x\mathsf{\Gamma }\left(\beta \right)}}$

). All distributions were adjusted using R version 4.4.3 [52].

(ii) Goodness of fit: These tests were designed to evaluate the goodness of fit of the data to the tested distributions. For this purpose, the Kolmogorov–Smirnov (k-S) test, Nash–Sutcliffe Efficiency (NSE) [36,48,51], P-P plots, and BIC (Bayesian Information Criterion) [55] where used.

(iii) Runoff coefficient: The runoff coefficient (C) is defined as the proportion of precipitation that flows over the surface [48,50,56]. This is because not all rain that falls on a surface generates runoff, because there are losses due to infiltration, evaporation and retention of the surface, depending on the type of soil or material on which the rain is received. For this reason, in a rainwater harvesting system, the runoff coefficient should be as close as possible to 1, in order to promote the highest rate of surface runoff for rainwater storage [29]. A coefficient of 0.85 was applied to the design of the RHS system, based on estimates from previous geomembrane projects in the Maule and Valparaíso regions [29,50,56].

(iv) Determination of design precipitation: Once the adjusted CDF has been validated, it is possible to determine the design precipitation for a given probability of occurrence. It is recommended to work with a probability of exceedance of 0.9, equivalent to a return period of 1.1 years. In other words, the annual precipitation is expected to exceed the design precipitation in at least 9 out of 10 years, thus ensuring that the expected volume of water is captured during those years [29,48,56].

2.3. Dimensioning of the RHS

The relationship between the catchment area and storage capacity can be analyzed using two distinct approaches. When the volume of water to be stored is predetermined, the corresponding catchment area must be calculated to ensure sufficient water is collected. Conversely, if the catchment area is fixed, the volume of water that can be captured and stored is constrained by this parameter. In both cases, the following expressions apply [29,48,57]:

$$Ca={\displaystyle \frac{Vc}{P\times C}}\vee Vc=P\times C\times Ca$$

(1)

where:

Ca:	Catchment area (m2).
Vc:	Water volume to be captured (m3).
P:	Design precipitation (m).
C:	Runoff coefficient.

2.4. Assessment of Installation Costs

To evaluate the installation costs of rainwater harvesting systems (RHS) in diverse scenarios, two systems were implemented: one on a hillside in the municipality of Arauco and another on a roof in the municipality of Florida. The costs of materials, supplies, and labor were documented for each project. The accumulated volume of water ($/m³) was calculated based on the total cost and the design capacity of each system. This allowed for cost comparison and analysis of the economic viability of the two approaches.

2.5. Incorporation of Rainwater for Well Replenishment

Incorporation of rainwater from the storage tank into the well was monitored using depth probes. The probes were calibrated in millimeters and were appropriate for measuring the water table level in both artificial reservoirs and natural wells. Based on an initial analysis and the data collected, the volumes of water stored in the wells were determined and quantified in cubic meters.

2.6. Water Quality

The quality of the water stored in the accumulation tanks and subsequently directed to the wells for recharge in both systems was evaluated in accordance with Chilean regulations issued by the Ministry of Public Works (NCh 1333) for irrigation [58]. The objective of evaluating the water quality under the Chilean standard NCh 1333 was to ensure its suitability for agricultural irrigation. Water samples were submitted to accredited laboratories for analysis. The parameters selected to evaluate water quality corresponded to those established as critical by the Chilean standard NCh 1333, considering their relevance to agricultural irrigation and their capacity to represent key chemical groups: physicochemical, heavy metals, dissolved salts, and microbiological parameters.

2.7. Potential Use of RHS at a Regional Level

To evaluate the potential use of rainwater harvesting systems for well replenishment at a regional level, a frequency analysis was conducted using the CR2met raster of interannual cumulative precipitation from Centro de Ciencia del Clima y la Resiliencia-CR2 (https://www.cr2.cl/; accessed on 7 November 2024). This raster models the daily regional precipitation for the period 1960–2021 with a pixel size of 0.05° (5.5 km) [59]. This allowed for the calculation of the design precipitation (probability of exceedance of 0.9) for the area, thereby identifying the optimal points for the implementation of the RHS.

3. Results

3.1. Runoff Coefficient and Design Precipitation

The runoff coefficient depends on the surface on which runoff occurs. In this study, a geomembrane was used as a waterproofing cover in the Arauco commune, and a zinc roof was used in the Florida commune. In both cases, a runoff coefficient of 0.85 was used [29,48,50]. For each site, a nearby rain gauge station was selected and an annual rainfall series was obtained and adjusted to CDF.

Table 2. Summary statistics of the analyzed stations. n: Sample size.

Parameters	RHS Arauco	RHS Florida
Mean (mm)	1144.2	937.8
Standard deviation (mm)	253.0	260.2
n	20	28

summarizes the data for each rain gauge.

The evaluated CDFs show a good fit for the precipitation data, achieving NSE values above 0.95 and p-values above 0.05 (

Table 3. Goodness of fit test results. K-S: Kolmogorov–Smirnov (p-value), NSE: Nash–Sutcliffe Efficiency, BIC: Bayesian Information Criterion.

RHS	GoF Test	Gumbel	Log-Normal	Gev	Log-Pearson III
Arauco	NSE	0.96	0.95	0.96	0.96
	K-S	0.91	0.72	0.88	0.83
	BIC	281	281	284	284
Florida	NSE	0.96	0.96	0.97	0.97
	K-S	0.46	0.39	0.75	0.67
	BIC	400	399	399	400

) in the Kolmogorov–Smirnov test (i.e., the selected CDFs can be used to model the data). This is further supported by the P-P plots for each CDF (Figure 3 and Figure 4).

3.2. Installation Costs

Under the current water resource crisis, nationally and regionally, the agricultural sector and communities are affected. The construction of rainwater harvesting systems is an alternative source of water supply in places where it is not possible to install water distribution pipes or where water transfer services by water trucks are scarce and involve a high cost for municipalities. The cost of the systems implemented, when calculating the value per accumulated volume ($/m³), shows that the system implemented in the municipality of Arauco is more cost effective than the roofing work in the municipality of Florida (

Table 4. RHS implementation costs differentiated by scenario.

Item	RHS Arauco (Hillside)	RHS Florida (Roof)
Materials and supplies	7,770,000 CLP (8783.7 USD)	6,200,000 CLP (7008.9 USD)
Labor	1,554,000 CLP (1756.8 USD)	1,240,000 CLP (1401.8 USD)
Total	9,324,000 CLP (10540.5 USD)	7,440,000 CLP (8410.7 USD)
$/m3	233,100 CLP (263.512 USD)	744,000 CLP (841.068 USD)

). Table 4 lists the construction costs for both the projects.

A comparative analysis of the construction costs for the RHS per accumulated volume ($/m³) indicated that the system implemented in Arauco was more cost-effective than the roofing system in Florida. This suggests that smaller projects may not be the most appropriate for construction. The higher cost per cubic meter of water stored in smaller systems can be attributed to economies of scale, as larger systems distribute fixed costs (e.g., installation, labor, and materials) over a larger volume of water, thereby reducing the unit cost. Additionally, smaller projects may require more frequent maintenance and have lower overall water collection efficiency because of limited catchment areas. However, implementing large-scale projects is not always feasible because of geographical constraints, existing structures on the site, or limited financial resources at the time of construction.

A simplified NPV was also calculated, considering only the fixed costs, such as construction costs, water transportation costs (including the cost of acquiring potable water, truck rental, and maintenance costs for the infrastructure). This resulted in an NPV of $9,564,745 ($10,812.7 USD) for the Florida area and an NPV of $2,216,616 ($2505.8 USD) for the Arauco area, with an investment payback period of 6 and 4 years, respectively. These data confirm that the implementation of rainwater harvesting systems is financially viable and highly profitable, with a rapid return on investment and sustainable long-term benefits.

3.3. Design and Implementation of the RHS Well Recharge System

The dimensions of the RHS were established using Equation (1), the design rainfall for each locality (

Table 5. Design precipitation, estimated catchment area, and volume.

RHS	Variable	Gumbel	Log-Normal	GEV	Log-Pearson III
Arauco	Design precipitation (m year−1)	0.861	0.854	0.860	0.852
	Area (m2)	55	55	55	55
	Volume (m3)	40	40	40	40
Florida	Design precipitation (m year−1)	0.611	0.617	0.607	0.604
	Area (m2)	20	20	20	20
	Volume (m3)	10	10	10	10

) and the respective runoff coefficients. The volume to be captured was defined according to the dimensions of the hydroaccumulators: a 40 m³ flexible tank in the municipality of Arauco and a 10 m³ polyethylene tank in the municipality of Florida. The recharge system consisted of pipes that carried rainwater from the hydroaccumulator to the well. For this purpose, electric pumps were installed to move the water at distances of approximately 270 m and 12 m for the RHS in the municipalities of Arauco and Florida, respectively.

The CDFs were assessed with a probability of 0.1 to obtain the design precipitation values (Table 5).

The evaluation of the RHS system was conducted between April and June 2023, during which both the well volume and accumulated volume in the RHS system were recorded. Initially, it was observed that at the commencement of the recharge process, the well volume exhibited an increasing trend, whereas the RHS volume decreased in accordance with the transfer of water to the well (Figure 5).

3.4. Water Quality Measurements from RHS

The results of water analysis showed that the experimental systems collected high-quality water. The concentrations of the parameters measured were generally within the limits of the Chilean standards for irrigation (NCh 1333). With respect to heavy metals and trace elements, including arsenic (As), cadmium (Cd), chromium (Cr), mercury (Hg), and lead (Pb), the detected concentrations in both RHS systems were markedly low, predominantly below the detection limit, suggesting minimal contamination by heavy metals. Parameters associated with salts and inorganic compounds, encompassing chlorides (Cl⁻), fluorides (F⁻), sulfates (SO₄²⁻), and total dissolved solids (TDS), are substantially below the maximum permissible limits. Microbiological indicators, specifically fecal coliforms, exhibited extremely low levels in both systems (significantly below the permitted limit of 1000 NMP/100 mL). These findings demonstrate the efficacy of the system in preventing contamination of collected water. The observed water quality enables the safe injection of captured water into wells and facilitates direct agricultural irrigation from the collection system (

Table 6. Selected water quality parameters according to the Chilean standard NCh 1333 for the RHS systems in Arauco and Florida.

Element	Unit of Expression	Maximum Limit	RHS Arauco	RHS Florida
Temperature	°C	* V. N. + 3	9.3	9.2
pH	---	5.5–9.0	8.02	8.49
Arsenic (As)	mg/L	0.1	<0.001	<0.002
Cadmium (Cd)	mg/L	0.01	<0.002	<0.002
Cyanides (CN−)	mg/L	0.2	<0.05	<0.01
Chlorides (Cl−)	mg/L	200	4.5	2,3
Copper (Cu)	mg/L	0.2	<0.008	<0.008
Fecal Coliforms	NMP/100 mL	1000	<2.0	<1.8 *
Chromium (Cr)	mg/L	0.1	<0.007	<0.007
Fluoride (F−)	mg/L	1	0.02	0.03
Iron (Fe)	mg/L	5	<0.032	<0.032
Manganese (Mn)	mg/L	0.2	0.01	<0.05
Mercury (Hg)	mg/L	0.001	<0.001	<0.001
Lead (Pb)	mg/L	5	<0.018	<0.018
Total Dissolved Solids	mg/L	500	<9.2	<9.3
Sulfate (SO42−)	mg/L	250	<1.9	<1.9
Zinc (Zn)	mg/L	2	0.61	0.675

* Escherichia coli.

).

3.5. Potential Use of RHS

The spatial distribution of the design precipitation in the Biobío region (Figure 6) exhibited significant variability, with values ranging from 688 to 2491 mm year⁻¹. The areas with the highest precipitation (>1000 mm year⁻¹) were primarily located in two sectors: one near the central to southeastern region and another clearly defined in the extreme southeast of the region, both identified as favorable zones for RHS implementation. Conversely, the northern and western areas presented lower precipitation levels, suggesting that these regions might require larger catchment areas or greater storage capacities for efficient rainwater harvesting. Regarding precipitation levels, RHS Arauco (<1300 mm) exhibited higher precipitation than RHS Florida (<1000 mm).

4. Discussion

In the context of climate change and prolonged drought [18,19], it is essential to implement innovative tools and technologies to address water scarcity [60]. Rainwater harvesting systems (RHS) have the potential to increase water availability during dry periods by capturing and storing rainwater [14,61]. The accumulated water can be used for multiple purposes, including domestic activities, agricultural irrigation, and with appropriate treatment and human consumption [14].

An aspect to consider in the implementation of RHS is their efficiency, which is determined by three main factors: precipitation in the area, physical characteristics of the catchment area (size and runoff coefficient), and storage capacity of the hydro-accumulator [62]. To mitigate the effect of variability in annual precipitation, the hydrological design of the rainwater storage systems installed in the municipalities of Florida and Arauco was based on a 90% exceedance probability (i.e., the designed precipitation will exceed 9 out of 10 years). Incorporating this factor into the design of an RHS requires increasing the catchment area to ensure capture of the intended volume. This criterion has the disadvantage of increasing construction costs, as the RHS catchment area expands when the exceedance probability is increased. While this enhancement provides a safety factor against prolonged droughts, using high exceedance probabilities (0.99) significantly impacts geomembrane costs and must therefore be carefully balanced during the design phase of the structure.

It is important that the cumulative distribution function (CDF) adequately models the precipitation data series as the design precipitation is estimated based on it. If the CDF is inaccurate, the calculations are not optimal [29,50]. Four CDFs (Gumbel, Log-normal, GEV, and Log-Pearson Type III) were evaluated. The results of this analysis indicate that, according to the BIC (Table 3), the best-fitting distributions for RHS Arauco are Gumbel and Log-normal, while for RHS Florida, Log-normal and GEV perform best. However, considering that all CDFs achieved Nash–Sutcliffe Efficiency (NSE) values above 0.95, were accepted by the Kolmogorov–Smirnov (K–S) test (Table 3), and showed a good fit in the P–P plots (Figure 3 and Figure 4), along with the practical advantages of using the Gumbel distribution—which is a two-parameter model, widely used in Chile, and easy to apply—it was chosen as the preferred distribution for estimating design precipitation [63]. At the end of the rainy season, both tanks reached 100% capacity.

Similarly, to minimize water loss in the system, the catchment area was waterproofed with a geomembrane (RHS Arauco). This material has a runoff coefficient of 0.8 (i.e., 80% of the captured volume flows into the hydroaccumulator). The selection of materials with high runoff coefficients improves the overall efficiency of the RHS [64,65,66,67]. The design of the RHS, considering the aforementioned factors (design precipitation, catchment area size, and runoff coefficient), allows the implementation of RHS that are resilient to precipitation variability. This ensures the filling of the hydroaccumulators during the winter period, the rainiest season in the Mediterranean zone, increasing local water availability.

A comparative analysis of construction costs for RHS per accumulated volume ($/m³) indicated that the system implemented in Arauco was more cost-effective than the roofing system in Florida. This suggests that smaller projects may not necessarily be the most appropriate for construction. This finding aligns with Istchuk and Ghisi [68], who state that “larger catchment areas can increase the volume of rainwater collected, potentially reducing the cost per unit volume of water harvested.” Nevertheless, it is not always feasible to implement a large-scale project because of geographical constraints, existing structures on the site, or limited financial resources at the time of project implementation. In general, families with greater financial resources tend to be more inclined to purchase rainwater harvesting systems (RHS), which can influence the perceived cost-effectiveness of these installations [69]. While installing a rainwater harvesting system may require a significant initial investment owing to infrastructure and installation costs, in the long run, it can help reduce operational expenses, especially in areas where the water supply is expensive or limited. In the municipality of Florida, filling a 10 m³ water tank costs CLP $786,800 (approximately USD $888.5). Harvesting rainwater during three annual events results in annual savings of CLP $2,360,400 (USD $2668.4). Taking into account an annual maintenance cost of CLP $50,000 (USD $56.5), a discount rate of 6% [50], and a system lifespan of 10 years, the Net Present Value (NPV) is estimated at CLP $9,564,745 (USD $10,812.7), with a payback period of 4 years.

In the municipality of Arauco, filling the tank costs CLP $814,000, and it is filled twice a year, resulting in annual savings of CLP $1,628,000 (USD $1840.4). The infrastructure cost was CLP $9,324,000 (USD $10,540.5), with estimated annual maintenance of CLP $60,000 (USD $67.8). Using the same discount rate, the system’s NPV reaches CLP $2,216,616 (USD $2505.8), with a payback period of 6 years. These results confirm that rainwater harvesting systems are financially viable, with relatively quick investment recovery and long-term sustainable benefits.

Our pilot test evaluated the use of technologies such as rainwater harvesting for recharging wells and irrigation purposes, thereby extending water availability. As a trial, two RHS were installed in the Biobío region, detailed as follows. (a) The RHS implemented in the municipality of Arauco was located at an elevated terrain level because this area had the appropriate dimensions for its installation. The construction of the catchment area required clearing and cleaning the site, compacting the soil, and creating a slope to facilitate water flow. Subsequently, this area was waterproofed with a geomembrane, thereby creating an RHS catchment area. The conveyance system consists of hoses that connect the catchment area to the hydroaccumulator and PVC pipes that transport water from the hydroaccumulator to the well. Its functionality was verified through field tests, and no leakage or installation issues were detected. Regarding the storage zone, which is the reservoir where water is stored, a 40 m³ flexible tank was installed on the previously leveled and compacted ground. (b) In the Florida RHS, a system was installed that captures rainwater through a pre-existing zinc roof and then distributes it via PVC pipes to the storage tank (10 m³). The construction yielded positive results, as the first rain event allowed the verification of water runoff into the polyethylene tank. To distribute the stored water in both RHS, an electric pump was installed to transport water from the hydro-accumulator to the recharge system and wells. The operation of this system was reviewed and tested, yielding good results in terms of water pressure at the well outlet.

The results of this pilot test were consistent with the conclusions of Sangüesa and Vallejos [29], who evaluated this technology in the Valparaíso and Maule regions. They determined that these systems enable water accumulation in central Chile [29]. However, stored water can also be used for irrigation of plantations at the scale of small producers [50,56], which can generate economic income from these crops by scaling up their businesses or integrating them into higher-level commercial chains. This aligns with the implicit objectives of the project, which aim to achieve economic benefits, and demonstrates that this type of technology contributes to the development of small-scale family farming in the region.

Likewise, the combination of RHS technology with well recharge has the potential to increase water supply in arid areas [12,70,71,72]. In this regard, Kashiwar et al. [73] evaluated the feasibility of this technology in Maharashtra (India), confirming that RHS are an effective option for storage, consumption, and well recharge. Netzer et al. [74] also determined the potential of using rainwater collected from building roofs for aquifer recharge in Mediterranean climates. To investigate this, they used both dry and water-filled wells and, found that the infiltration capacity in dry wells increased during winter, whereas in water-filled wells, it remained constant.

Although RHS technology has proven to be a viable alternative for aquifer recharge, its application is limited. A key factor in the effectiveness of this process is soil permeability, because low conductivity restricts the infiltration of stored water [75]. In this regard, soil composition, particularly texture, plays a key role in the capacity for water injection into the aquifer. Previous studies have indicated that sandy-clay soil profiles exhibit more efficient recharge rates, suggesting the need to evaluate soil characteristics before implementing water harvesting systems for this purpose [76].

These findings demonstrate that this technology can be used for aquifer recharge and to reduce urban runoff. However, Olivares and Herrera [75] argue that this technology is not universally applicable. In low-permeability areas, they pointed out that the advantages of using shallow wells are offset by the costs of aquifer monitoring and recommended the use of direct injection methods in such cases. This represents a limitation of the technology, which should be addressed through studies and pilot tests in different regions of the country.

The quality of water for well recharge and furrow irrigation is limited in traditional systems, as the transported water may contain contaminants such as excess nitrates, heavy metals, or pesticides [77,78]. In our research, the analysis of the quality of accumulated water demonstrated that experimental rainwater harvesting systems collected high-quality water, with concentrations of physicochemical parameters, heavy metals, inorganic salts, and microbiological indicators consistently within the limits established by the Chilean irrigation standards (NCh 1333). Our study demonstrates the effectiveness of these systems in preventing contamination of the collected water, allowing for its safe injection into wells and direct use for agricultural irrigation, consistent with the findings of Choi et al. [79], Vialle et al. [80], and Richards et al. [81]. Although our study’s objective was to collect water for well recharge and potential agricultural use, in the context of water scarcity, the stored water could also be used for domestic purposes, providing a more rigorous evaluation, including microbiological assessments such as Escherichia coli counts [82]. Additionally, based on these results, treatments such as the controlled-dose addition of chlorine could be applied to use the harvested water as drinking water [83,84].

The results of the regional frequency analysis show a high applicability of this technology in the region, as the designed precipitation amounts were adequate for accumulating large volumes of water (Figure 6). Consequently, the implementation of this technology has emerged as an effective tool to counteract the effects of climate change and as an adaptive measure. This is especially important because the region is projected to experience a decrease of approximately 30% in the average annual precipitation [85,86,87,88].

Similarly, from a sustainability perspective, RHS offer advantages over well construction, particularly when used as a water source for households or on a small scale [89]. Abd-Elaty et al. [12] indicate that this technology is efficient for aquifer recharge and has the potential to reduce surface runoff in the area. This reduction in surface runoff represents a benefit not considered in the present study but one that would be interesting to investigate in the future, especially in urban areas. In these areas, rooftops can be adapted to capture and redirect rainwater into an underground storage system (hydroaccumulator). The captured water can then be used for irrigation and maintenance of parks and other urban green spaces [90]. While this study provides valuable insights into the feasibility and performance of RHS for potential well recharge and agricultural irrigation, it did not include a control site without RHS for direct comparison. Incorporating a control scenario in future research would allow for a more precise evaluation of the relative improvements achieved through the implementation of the RHS. By monitoring groundwater levels and water availability in locations without RHS, future studies could more rigorously quantify the direct impact of these systems on aquifer recharge. Additionally, long-term assessments incorporating hydrological modeling and comparative field data from control and intervention sites would further refine our understanding of RHS effectiveness in different climatic and hydrological contexts. Future research should investigate the scalability and broader applicability of the RHS by integrating interdisciplinary perspectives. Collaboration with agronomists and economists could yield valuable insights into the socioeconomic feasibility of implementing RHS on a larger scale. This entails evaluating the long-term financial viability, potential incentives for adoption, and impact of these systems on rural livelihoods. Furthermore, policy and regulatory considerations should be examined to identify potential barriers and opportunities for the widespread adoption of RHS as a climate adaptation strategy. These interdisciplinary approaches would contribute to a more comprehensive understanding of the role of RHS in sustainable water resource management and its potential integration into broader agricultural and environmental policies.

One significant limitation of this study is the limited number of pilot rainwater harvesting systems (RHS) evaluated. The two systems analyzed were located in geographically adjacent areas within the Biobío region, which may constrain the applicability of the findings to other regions with distinct climatic and hydrological conditions. Although both RHS are situated in different climatic zones, their proximity to regional boundaries may result in minimal climatic differences, thereby limiting the variability of the conditions assessed in this study. The effectiveness of RHS may be influenced by factors such as variations in precipitation patterns, soil permeability, and local water demand, highlighting the need to evaluate these systems in diverse contexts to derive broader and more generalizable conclusions [31,91]. To address this limitation, future research should broaden the scope of the analysis to encompass pilot sites across a wider range of geographical and climatic conditions. Conducting long-term evaluations in Mediterranean, arid, and semi-arid regions, as well as in areas characterized by diverse hydrological regimes, would facilitate a more comprehensive understanding of the performance, sustainability, and scalability of the RHS. Furthermore, assessing the economic feasibility and maintenance requirements of RHS under various conditions would enhance their potential for large-scale implementation as a climate change adaptation strategy. One critical aspect not explicitly addressed in this study is the long-term maintenance requirements of the RHS [14]. The sustainability and operational efficiency of these systems depend on the periodic cleaning of catchment surfaces, regular inspection of conveyance systems, and maintenance of storage tanks and filtration components. Future research should assess the costs, labor demands, and technical challenges associated with maintaining the RHS over extended periods. Understanding these factors is essential for ensuring the long-term viability and scalability of these systems, particularly in rural and agricultural settings, where resource availability may be constrained.

5. Conclusions

Water scarcity experienced by small rural farmers in recent decades has introduced significant uncertainty to their economies and well-being. In this context, rainwater harvesting systems (RHS) have demonstrated their capacity to increase the water supply in communities, particularly for agricultural use. In this project, we observed that wells often dry up during the summer period; thus, implementing these systems not only benefits small-scale agriculture but also contributes to water storage and well recharging. Our hydrological design estimated annual precipitation values of 861 mm in Arauco and 611 mm in Florida, supporting the implementation of RHS. The two pilot systems successfully captured and stored 40 m³ of rainwater in Arauco and 10 m³ in Florida, with monitored recharge confirming the transfer of stored water into wells. Considering the anticipated impacts of climate change in Chile’s Mediterranean region, widespread adoption of RHS could be vital for addressing the expected decline in water availability. Moreover, we found that the collected water could be suitable for domestic use if properly treated, underscoring the multiple benefits of these systems. The economic feasibility analysis revealed that the cost per cubic meter of stored water was $263.51 USD/m³ in Arauco and $841.07 USD/m³ in Florida, demonstrating that larger systems are more cost-effective owing to economies of scale.

Among the evaluated applications, our study confirmed the feasibility of using harvested rainwater for irrigation, without ruling out its potential for aquifer recharge and domestic consumption following adequate treatment. Having established the viability of irrigating subsistence crops, the next step is to evaluate specific crop varieties, assess water treatment methods that incorporate nutrients, and monitor crop responses. Such measures could enable small farmers, who previously relied on other, often unpredictable, water sources, to maintain and expand their agricultural activities in a sustainable and prolonged manner. Finally, we conclude that for these initiatives to succeed, it is essential to establish minimum engineering designs, such as those proposed in this study, prior to constructing the RHS. By doing so, the infrastructure can be optimized to ensure the efficiency and overall success of the system.