Assessing the potential of domestic reclaimed water for agricultural irrigation in Taiwan Open Access

Taiwan's unique geographical and climatic conditions contribute to its complex water resource challenges. The island features steep and rugged terrain, with 70% of its annual rainfall occurring during the summer plum rain season and typhoon events, while winter precipitation is significantly lower (Hsu et al. 2020). The average annual rainfall in Taiwan from 1949 to 2020 is approximately 2,500 mm, which is 2.5 times the global average (WRA 2023). Despite this seemingly abundant rainfall, the uneven temporal distribution of precipitation ranks Taiwan as the 18th most water-scarce country in the world (Tseng et al. 2012; Scotti 2020).

Long-term climate analyses have revealed significant regional and temporal variations in Taiwan's precipitation patterns. Hsu & Chen (2002) found that, over the past century, rainfall has increased in northern Taiwan while decreasing in the south, with a notable reduction in the number of rainy days across the entire island. Furthermore, Huang et al. (2003) reported that small-scale droughts (defined as periods of no rainfall for 50 consecutive days) in the western plains of Taiwan (from Hsinchu in the north to Pingtung in the south) have expanded to upstream watersheds, indicating an increasing likelihood of large-scale droughts (defined as periods of no rainfall for 100 consecutive days). Additionally, the variability in the timing and spatial patterns of streamflow is significant (Yu et al. 2002). Climate change is expected to exacerbate these trends, affecting Taiwan's river flows by reducing runoff during the dry season (November–April) and increasing it during the wet season (May–October) (Li et al. 2006). These changes will likely intensify the frequency of both droughts and floods, impacting water resources supply and demand and increasing the costs associated with water resource development, transportation, treatment, and distribution (Edward 2024).

Water consumption patterns in Taiwan further complicate the issue. Between 2001 and 2022, agricultural water use accounted for 71.28% of the total water supply, while industrial and domestic water consumption represented 9.46 and 19.26%, respectively. Over the past decade, Taiwan's total water demand has increased by approximately 4.6%, with urban and industrial demand rising by 45.72 and 14.86%, respectively, while agricultural water demand declined by 4.0% (Chen & Hsu 2010). The primary sources of water supply include dams, rivers, and groundwater, contributing 33, 44, and 23% of the total water supply, respectively (Chen & Hsu 2010). However, Taiwan's pricing mechanisms do not reflect the varying costs of water extraction, treatment, and distribution. The uniform retail price of tap water is USD 0.352 per cubic meter, whereas the actual cost of water processing is approximately USD 0.365 per cubic meter (Lee et al. 2018). Additionally, Taiwan's low water pricing structure results in inefficient water use, particularly in agriculture, where irrigation water is priced at only NT$ (New Taiwan dollar) 0.28 per cubic meter, significantly lower than non-agricultural water rates. This low price for agricultural water leads to substantial waste, especially during the rice cultivation period from February to September (Chen & Hsu 2010).

Water quality deterioration has become a critical issue in recent years, particularly in densely populated areas. Sources of contamination include industrial pollution, aquaculture activities, and agricultural runoff, which contribute to heavy metal contamination in natural water bodies (Zhang et al. 2018). Secondary releases of chemical fertilizers and pesticides further exacerbate pollution levels (Du et al. 2005). These localized anthropogenic activities have led to increased degradation of river and lake water quality, heightening the risks associated with using natural water sources for irrigation (Kumarathilaka et al. 2018). Given that up to 80% of Taiwan's agricultural irrigation water is sourced from rivers, pollution poses a significant threat to farmland and food safety. According to a 2020 report by Taiwan's Ministry of Environment, there are 7,404 polluted farmland sites (approximately 1,190.6 ha) across the country, with most located in Changhua County (53.8%), followed by Taoyuan City (29.8%) and Taichung City (7.8%) (MOENV-EMA 2021). The contamination of irrigation water with heavy metals necessitates stringent risk management to ensure food safety (Jie et al. 2021). Research by Zhang et al. (2013) also confirmed that heavy metal pollution in farmland soil is primarily caused by the irrigation of polluted water sources.

On a global scale, population growth, rapid urbanization, and climate change have exacerbated water scarcity, making access to sufficient and safe freshwater one of humanity's greatest challenges (Sheidaei et al. 2016). Rising populations increase food demand, necessitating significant freshwater allocations to agriculture (Phogat et al. 2020a, b). However, in many arid and semi-arid regions, water demand already exceeds available surface and groundwater supplies (FAO 2008; Famiglietti 2014; UN Environment 2019). To mitigate water shortages, treated urban wastewater is increasingly recognized as an alternative water source for crop production (Hamilton et al. 2007; Qadir et al. 2010; Grattan et al. 2015; Otoo & Drechsel 2018). Wastewater reuse has been widely implemented, particularly in water-scarce regions such as the Mediterranean, where treated wastewater accounts for 5–12% of total water use (Kidd et al. 2007; Agrafioti & Diamadopoulos 2012; Kellis et al. 2013). Reclaimed water provides multiple benefits, such as alleviating pressure on freshwater supplies, reducing costs and energy consumption (Meneses et al. 2010), recycling nutrients to enhance soil fertility (Hanjra et al. 2012; Becerra-Castro et al. 2015), minimizing sewage discharge into the environment (Meneses et al. 2010; Plumlee et al. 2012), and avoiding the environmental impacts associated with developing new water sources (Ormerod & Scott 2013).

Despite these benefits, long-term reclaimed water use presents challenges, such as increased soil salinity and the risk of soil alkalinity hazards (Assouline et al. 2016; Bardhan et al. 2016; Qian & Lin 2019; Phogat et al. 2020a, b). Moreover, irrigation with heavy metal-contaminated wastewater can lead to the accumulation of heavy metals in soil, increasing their uptake by crops and raising food safety concerns (Liu et al. 2005; Muchuweti et al. 2006; Rothenberg et al. 2007; Arora et al. 2008; Khan et al. 2008). These risks underscore the need for appropriate wastewater treatment and management strategies (Mapanda et al. 2005; Rattan et al. 2005; Al Omron et al. 2012; Mohammed & Folorunsho 2015). Properly treated and managed reclaimed water can serve as a sustainable irrigation source, alleviating environmental and economic pressures on agriculture (Jiménez 2006; Jovanovic 2008; Holt-Giménez et al. 2012; Jaramillo & Restrepo 2017).

Taiwan faces dual challenges regarding water quantity and quality. In response, the Water Resources Agency of the Ministry of Economic Affairs proposed four flood and drought control measures in 2021: expanding water sources, reducing consumption, establishing backup supplies, and enhancing water resource management. Given that industrial wastewater may contain pollutants unsuitable for agricultural irrigation, reclaimed water from domestic sewage treatment plants presents a viable alternative. Therefore, this study evaluates Taiwan's potential for utilizing reclaimed water from existing domestic sewage treatment plants, assessing immediate and future supply capacities to contribute to sustainable water resource management and agricultural resilience.

According to water usage statistics from Taiwan's Water Resources Agency, between 2001 and 2022, Taiwan's average total water consumption was 17.28 billion tons annually. Of this, agricultural water use averaged 12.33 billion tons (71.28%), domestic water use was 3.32 billion tons (19.26%), and industrial water use was 1.63 billion tons (9.46%). Agricultural water use can be further divided into irrigation, aquaculture, and livestock water, accounting for 89.86, 9.42, and 0.72%, respectively. Notably, agricultural water usage consistently exceeded 70% of the total water consumption annually, even in years with scarce rainfall, underscoring the importance of Taiwan's agricultural sector.

According to the 2022 annual report of the Water Resources Agency, the irrigated agricultural land area in Taiwan totals 383,715 ha, of which 364,736 ha (95.05%) are managed by the Irrigation Agency under the Ministry of Agriculture, and the remaining 18,979 ha (4.95%) are managed by Taiwan Sugar Corporation farms. The Irrigation Agency operates 17 Management Offices responsible for overseeing irrigation areas and allocating agricultural irrigation water within their respective administrative regions. In the northern region, there are seven offices, such as Yilan, Peikee, Liugong, Chising, Taoyuan, Shihmen, and Hsinchu, managing a total irrigation area of 64,976 ha (18%). The irrigation area includes Keelung City, Taipei City, New Taipei City, Taoyuan City, Hsinchu County and City, and Yilan City. In the central region, five offices, such as Miaoli, Taichung, Nantou, Changhua, and Yunlin, manage an irrigation area of 151,132 ha (42%). The irrigation area includes Miaoli County, Hsinchu County and City, Taichung City, Nantou County, Chanhua County, Yunlin County, and Chiayi County. In the southern region, three offices, such as Chianan, Kaohsiung, and Pingtung, manage an irrigation area of 117,973 ha (32%). The irrigation area includes Tainan City, Chiayi City and County, Kaohsiung City, and Pingtung County. In the eastern region, two offices, such as Hualien and Taitung, manage an irrigation area of 30,655 ha (8%) (Table 3). The irrigation area includes Pingtung County and Hualien County.

The reclaimed water sources considered in this study are strictly limited to domestic wastewater, primarily originating from households. Wastewater is collected through household sewer connections, transported via pipelines to sewage treatment plants, and undergoes secondary or tertiary treatment, with only a few instances of primary treatment. If not reused, the treated effluent is discharged into rivers and the ocean. Therefore, this study advocates for supplying the treated effluent to agricultural irrigation zones downstream of sewage treatment plants. The proposed application method suggests connecting the discharge outlets of sewage treatment plants to nearby existing irrigation channels. This approach allows irrigation to be conducted by gravity flow, utilizing natural topographical slopes, and is recommended by Taiwan's agricultural sector as a feasible application.

To assess the efficiency and contribution of reclaimed water in agricultural irrigation, this study adopted a framework where the reclaimed water (W_R) from water reclamation centers served as the water supply endpoint, while the agricultural irrigation demand within the irrigation areas constituted the water demand endpoint. The planned water use (W_I) and actual water intake (W_A) within the irrigation areas managed by the offices were considered as the irrigation demand and actual irrigation water use, respectively.

To further analyze the effectiveness of reclaimed water applications, the study established two scenarios. Scenario 1: the immediate supply capacity at the current stage and Scenario 2: the potential supply capacity over the next five years based on the total designed capacity of existing facilities.

Data on planned irrigation water and actual water intake were collected from the 17 irrigation management offices under the Taiwan Irrigation Association for the years 2010–2019. The results indicate that the average planned irrigation water amount (W_I) over this decade was 15.26 × 10⁹ m³/year. Among the different water resource regions, the central region had the highest planned irrigation amount at 7.76 × 10⁹ m³/year. The planned irrigation water amounts for other regions were relatively similar, ranging from 2.30 to 2.83 × 10⁹ m³/year. The central region accounted for 51% of the total planned irrigation water, followed by the southern region (19%), the eastern region (15%), and the northern region (15%) (Table 5). Taiwan's average annual actual water intake was 10.96 × 10⁹ m³, with an annual water deficit of 4.3 × 10⁹ m³. The central region had the highest actual water intake at 4.81 × 10⁹ m³/year, but also the largest water resource gap which was 2.95 × 10⁹ m³/year. The northern and southern regions had annual deficits of 4.1 × 10⁸ and 9.7 × 10⁸ m³, respectively. Notably, the eastern region's actual water intake exceeded the planned amount, indicating no water shortage in that area.

To evaluate the contribution of reclaimed water to agricultural irrigation, two scenarios were analyzed: current conditions (Scenario 1) and maximum potential supply of reclaimed water (Scenario 2) (Table 6). In Scenario 1, which considers the utilization of current sewage treatment capacity, reclaimed water could supply 8% of the planned irrigation demand and 11.13% of the actual water intake. The northern region leads in the contribution of planned irrigation water from reclaimed water at 33.24%, followed by the southern region at 12.83%. Contributions to actual water intake remain highest in the northern region (40.36%), followed by the southern region (19.53%), with the central and eastern regions both below 2%.

In Scenario 2, assuming the maximum potential capacity utilization of sewage treatment plants, reclaimed water could supply 12.74% of the planned irrigation demand and 17.73% of the actual water intake. The northern region would contribute the most to planned irrigation water with reclaimed water at 46.14%, followed by the southern region (23.08%), while the central region contributes 2.68% and the eastern region just 1.08%. In terms of actual water intake, the northern region's contribution would be 56.02%, the southern region's 35.12%, and the central and eastern region's 4.33 and 1.02%, respectively.

The results of these scenario analyses demonstrate that, under current conditions, reclaimed water can supply only 8% of the planned irrigation demand, but this could increase significantly to 12.74% under Scenario 2. Similarly, the contribution to actual water intake would rise from 11.13% in Scenario 1 to 17.73% in Scenario 2. This suggests that reclaimed water from Taiwan's domestic sewage has the potential to significantly meet agricultural irrigation water demand. When combined with other water conservation measures, reclaimed water can play a critical role in mitigating the impact of droughts on agricultural water supply. Furthermore, this application is particularly suitable for replacing original water sources from heavily polluted rivers, thereby reducing agricultural pollution and soil leaching contamination.

Nitrogen is widely recognized as one of the key nutrients affecting the sustainability of aquatic ecosystems. Excessive anthropogenic nitrogen emissions can lead to the deterioration of water quality, resulting in eutrophication. The ammonia nitrogen load from reclaimed water under two scenarios was calculated (Table 7). For sewage treatment plants that do not provide effluent ammonia nitrogen concentration data, the ammonia nitrogen limit set by effluent standards (10 mg/L) was used as a reference. The results of Scenario 1 indicate that the annual ammonia nitrogen load produced across Taiwan is 9,145.46 tons, with the northern region contributing the most at 6,108.25 tons (66.79%), followed by the southern region at 26.87%, the central region at 4.12%, and the eastern region at 2.22%. Scenario 2 results show an annual ammonia nitrogen load of 13,321.36 tons nationwide, with the northern region still contributing the most at 7,927.7 tons (59.51%), followed by the southern region at 31.18%, the central region at 6.89%, and the eastern region at 2.42%. Combining the results from both scenarios, it is evident that the northern and southern regions contribute over 90% of the ammonia nitrogen load to water bodies. Therefore, if the effluent from these regions is effectively utilized for agricultural irrigation, it could significantly alleviate the pressure on the carrying capacity of water bodies.

Globally, 80% of wastewater is not adequately treated, yet it is used to irrigate 11% of the world's agricultural land, with even higher percentages in regions such as Latin America, South Asia, and Africa (Kookana et al. 2020). Reusing wastewater for irrigation can alleviate water scarcity and economic pressure in agriculture while increasing year-round water availability (Jiménez 2006; Jovanovic 2008; Holt-Giménez et al. 2012; Jaramillo & Restrepo 2017). Treated wastewater holds significant potential as an alternative water source for irrigation, especially in water-scarce regions (Howell et al. 2015). In areas facing water scarcity and the challenges of climate change, such as South Africa, wastewater reclamation has been adopted as a viable solution (Adewumi et al. 2010). In China and other arid regions, reclaimed water has been widely used for agricultural irrigation (Mapanda et al. 2005; Wang et al. 2007). Ballesteros-Olza et al. (2022) utilized reclaimed water in water-scarce regions of Spain and highlighted multiple initiatives launched by the European Union to promote the use of reclaimed water for irrigation, aiming to alleviate the pressure of climate change on regional water resources. Drechsel et al. (2022) argued that under climate change scenarios, the use of reclaimed water can enhance the resilience of regional water resources. The allocation and utilization of reclaimed water have been shown to help mitigate challenges related to agricultural water shortages while increasing the economic value and productivity derived from it. Trinh et al. (2013) evaluated wastewater reuse as an adaptation strategy to address water resource shortages, with findings indicating that treated wastewater could irrigate at least 22,719 ha of rice paddies.

In this study, we evaluated the planned and actual irrigation water in various regions, as well as the potential capacity of reclaimed water for agricultural irrigation (Tables 5 and 6). In Scenario 1, utilizing reclaimed water under current conditions could reduce the overall water deficit for the entire island from 28.1 to 20.1%, with a further reduction to 15.4% in Scenario 2. Among the various regions, the addition of reclaimed water would eliminate the water deficit in the northern region in both Scenario 1 and Scenario 2. Similarly, in the central region, the water deficit would decrease from 38.1 to 37.0% under current conditions and to 35.4% with the maximum potential supply of reclaimed water. In the southern region, the water deficit would decrease from 34.3 to 21.5% under current conditions and to 11.2% with the maximum potential supply of reclaimed water. These findings indicate that reclaimed water treatment plants have significant potential for agricultural irrigation in the northern and southern regions, effectively addressing the issue of irrigation water deficits.

Furthermore, based on the average irrigation water requirements per unit area for one season of rice paddy fields in Taiwan, it requires 29.54 × 10³ m³/ha in the northern region, 21.10 × 10³ m³/ha in the central region, 18.33 × 10³ m³/ha in the southern, and 50.47 × 10³ m³/ha in the eastern region (WRA 2022). Therefore, with the supplementation of reclaimed water for irrigation, an additional 25,834.5 ha of paddy fields in the northern region, 3,853.7 ha in the central region, 19,808.0 ha in the southern region, and 263.5 ha in the eastern region could be irrigated under the current capacity of sewage treatment plants. Under the maximum capacity of the sewage treatment plants, an even larger area could be irrigated: 35,857.6 ha in the northern region, 9,864.1 ha in the central region, 35,627.2 ha in the southern region, and 487.4 ha in the eastern region.

The utilization of reclaimed water for irrigation has been expanding in various regions, necessitating legislative oversight to ensure its sustainable management (Arienzo et al. 2009). Numerous studies have evaluated the implications of reclaimed water use in agricultural irrigation. For instance, Kiziloglu et al. (2008) reported that wastewater irrigation enhanced cauliflower and cabbage yields, indicating that untreated wastewater could be viable for short-term applications, whereas primary-treated wastewater may be more suitable for long-term agricultural uses. Similarly, Trinh et al. (2013) found that reclaimed water could supply up to 22% of crops' nitrogen requirements and 14% of their phosphorus needs. On an annual scale, wastewater reuse has the potential to reduce nitrogen discharge by 15–27% and phosphorus discharge by 8–17%, thereby enhancing water resource efficiency while mitigating environmental impacts.

Moreover, Ibekwe et al. (2018) demonstrated that the diverse functional microbial communities in reclaimed water contribute to critical soil processes such as nutrient and carbon cycling. Additionally, the presence of both suspended and dissolved organic matter in reclaimed water may enhance soil fertility, thereby promoting agricultural productivity. Mola et al. (2024) investigated the effects of reclaimed water irrigation on maize and lavender, reporting significant improvements in crop yield, stabilization of soil chemical properties, enhancement of nutrient cycling, and increased microbial diversity and stability. Furthermore, Alkhamisi et al. (2011) found that plants irrigated with wastewater were taller than those irrigated with freshwater, primarily due to the elevated nitrogen content and salinity in reclaimed water. Collectively, these findings underscore the dual benefits of reclaimed water irrigation in improving agricultural productivity and optimizing water resource utilization.

In this study, the annual ammonia nitrogen load from reclaimed water and the annual streamflow across different water resource regions were analyzed (Figure 3 and Table 7). Direct discharge of reclaimed water into rivers can elevate ammonia nitrogen concentrations. Under current conditions (Scenario 1), the estimated ammonia nitrogen concentrations contributed by sewage treatment plants are 0.37, 0.02, 0.13, and 0.01 ppm in the northern, central, southern, and eastern regions, respectively. If treatment plants operate at their maximum potential supply (Scenario 2), these concentrations are expected to increase to 0.48, 0.06, 0.23, and 0.02 ppm in the northern, central, southern, and eastern regions, respectively. According to the Taiwan RPI, ammonia nitrogen concentrations of less than 0.5 ppm, between 0.5 and 0.99 ppm, between 1 and 3 ppm, and greater than 3 ppm are classified as non-polluted, slightly polluted, moderately polluted, and severely polluted, respectively. This indicates that larger amounts of reclaimed water will result in higher ammonia nitrogen concentrations in rivers if not used for irrigation. Therefore, using reclaimed water for agricultural irrigation can reduce the costs associated with water resource management and alleviate the burden on sewage treatment plants (Jang et al. 2010).

The application of reclaimed water for irrigation helps alleviate water supply and demand pressures and has significant benefits in mitigating water scarcity crises. While wastewater irrigation is increasingly promoted by governments and regulatory agencies worldwide, two major concerns are associated with this practice (Becerra-Castro et al. 2015). They are (1) alterations in the physical, chemical, and microbial properties of the soil and (2) potential accumulation of chemical and biological contaminants. The former may influence soil fertility and productivity, while the latter poses risks to human and environmental health. Implementing reclaimed water irrigation necessitates integrated risk assessments to mitigate potential adverse effects. Moreover, farmers' acceptance of reclaimed water for irrigation and consumers' food safety concerns regarding reclaimed water-grown agricultural products are critical factors in achieving widespread adoption. Therefore, after confirming the technical feasibility and benefits of reclaimed water irrigation, the next key challenges lie in policy implementation and social acceptance:

• (1) Clarification of responsibilities and jurisdiction: The provision of treated effluent from sewage treatment plants for agricultural irrigation requires a clear and unified delineation of responsibilities among relevant authorities.

• (2) Elevating the decision-making authority: Since different agencies oversee reclaimed water management in Taiwan – the Ministry of the Interior's National Land Management Agency for water sources, the Ministry of Economic Affairs' Water Resources Agency for water policy, and the Ministry of Agriculture for agricultural irrigation – the promotion and decision-making of reclaimed water use in agriculture should be coordinated at the national level, under the Executive Yuan or the Office of the President, to ensure effective policy implementation.

• (3) Crop-specific water quality tolerance: Different crops have varying tolerances for water quality. Taiwan's current promotion of reclaimed water for irrigation primarily targets rice cultivation due to its high water demand and the feasibility of utilizing existing irrigation channel systems for water distribution. However, crops such as vegetables and fruits, which are consumed raw, may pose hygiene and safety concerns depending on the type of water-saving irrigation systems used (e.g., sprinkler or perforated pipe irrigation). Additionally, greenhouses and independent farms without existing irrigation systems present another limitation for the application of reclaimed water.

• (4) Water quality monitoring standards: The monitoring of water quality at sewage treatment plants is primarily based on discharge standards for rivers, which typically include parameters such as water temperature, pH, BOD, COD, SS, TP, TN, HNO₃⁻, anionic surfactants, oils and greases, residual chlorine, Escherichia coli, and various heavy metals. While some of these parameters overlap with the 19 required irrigation water quality standards, specific heavy metals must be monitored for irrigation use. If reclaimed water is to be used for irrigation, water quality testing must follow irrigation water quality standards, requiring additional parameters such as electrical conductivity, DO, chloride (Cl⁻), sulfate ⁠, sodium adsorption ratio, and residual sodium carbonate. These parameters must be tested regularly, either monthly or bi-monthly as per current regulations.

• (5) Ammonia nitrogen controversy: Ammonia nitrogen (NH₃-N) is the most contentious parameter in irrigation water quality standards. Taiwan's current limit for irrigation water is 3 mg/L, yet many river sources used for irrigation often exceed this threshold without reported adverse effects on crop growth. To enhance the applicability of reclaimed water for irrigation, the ammonia nitrogen standard may need to be reassessed. A differentiated tolerance level based on crop types could be considered to balance both crop protection and the broader adoption of reclaimed water for irrigation.

• (6) Public awareness and acceptance: Strengthening public education on the definitions of wastewater, sewage, and reclaimed water is essential. Continuous field trials on reclaimed water irrigation should be conducted to verify its positive effects on crop growth, yield, and food safety. Clear and transparent information campaigns can help build trust among farmers and consumers, ensuring that reclaimed water used under strict regulations for agricultural irrigation is safe. Encouraging farmers to use reclaimed water for irrigation and gaining consumer confidence in purchasing reclaimed water-grown crops (especially rice) will be crucial for large-scale implementation.

• (7) Optimizing water resource utilization through demand-based allocation: Future water resource allocation strategies in Taiwan should prioritize reclaimed water for agricultural irrigation, promote water recycling and conservation for industrial use, and reserve clean reservoir water primarily for domestic consumption. This balanced approach ensures a sustainable and resilient water resource management system.

This study highlights the potential of reclaimed water as a sustainable solution for Taiwan's agricultural irrigation shortages. Given Taiwan's uneven rainfall and climate change challenges, reclaimed water offers a viable alternative, particularly in the water-scarce northern and southern regions. This study assesses reclaimed water use across Taiwan, analyzing its impact at three levels, such as counties, irrigation districts, and water resource regions. Findings provide valuable insights for policymakers on wastewater treatment expansion and water management strategies such as water source blending, dilution, or rotational irrigation to ensure stable agricultural production.

Under current conditions, reclaimed water could reduce irrigation deficits from 28.1 to 20.1 and to 15.4% at the maximum capacity. The northern region has the highest potential, potentially eliminating its deficit entirely, while the central and southern regions also see substantial improvements. Additionally, reclaimed water could expand irrigated paddy fields by up to 82,836.3 ha, enhancing food security and resources. However, careful management is required to mitigate environmental risks, particularly ammonia nitrogen pollution from direct discharge. Prioritizing reclaimed water for irrigation over river discharge can enhance water efficiency while reducing pollution.

In conclusion, reclaimed water can significantly improve Taiwan's agricultural resilience by addressing shortages, increasing efficiency, and minimizing environmental impact. Strategic use of reclaimed water, supported by robust regulations, is essential for long-term sustainability.

Data cannot be made publicly available; readers should contact the corresponding author for details.

The authors declare there is no conflict.