Challenges and opportunities of using reclaimed water for agricultural irrigation in Spain: A hydro-economic analysis. 

Abstract

Growing pressure on water resources and climate uncertainty are driving the need for alternative water sources. In countries with severe water stress, such as Spain, the reuse of water from urban wastewater treatment plants has become a promising opportunity to secure and improve agricultural production. The use of reclaimed water in agriculture offers many significant economic and the environment benefits. In addition to preserving freshwaters, it increases the reliability of water supplies and provides a source of nutrients needed for crop growth and soil fertility. In recent years, the European Union and the Spanish government have promoted the reuse of reclaimed water for irrigation as part of their circular economy strategies. However, the uptake of this practice is still limited and so far deployed below its potential. This study uses a hydro-economic model to investigate the potential for reclaimed water reuse in agriculture and effective water resource management in the Western La Mancha aquifer in Spain. In this region, groundwater abstraction for irrigation exceeds aquifer recharge, leading to conflicts between rural socio-economic development and water conservation. In this context, reclaimed water reuse is seen as an alternative source to groundwater that can contribute to reduce over-exploitation. An economic optimization model is linked to the hydrology model WEAP (Water Evaluation And Planning system) to analyse management alternatives, that include full compliance with the current water abstraction regime and different levels of reclaimed water reuse from the region’s urban wastewater treatment plants (current level and full potential). Climate uncertainty is also simulated and represented by projected precipitation and temperature changes from a selection of global climate models under different representative concentration pathways (4.5 and 8.5). The results show that compliance with the abstraction regime can help to mitigate aquifer overexploitation. Reclaimed water reuse represents an additional effort for aquifer recovery, resulting in improved groundwater storage levels. Its effect is particularly relevant under climate change scenarios, although groundwater levels would show a downward trend. However, reusing reclaimed water for irrigation reduces effluent flows to rivers and has a negative impact on meeting the environmental needs of downstream wetlands. At the same time, water reuse could mitigate the negative impact of water scarcity on farm incomes, especially in municipalities with high-capacity treatment plants (> 1Mm3/year) where high value crops (vineyards, olives and horticultural crops) are grown.  Overall, this research evidence uneven impacts of reclaimed water reuse across the basin. Its contribution to reversing groundwater depletion is limited and should be understood as part of the solution, but not as the solution itself. Our results provide valuable insights into the economic and environmental implications of reclaimed water reuse and can support policy decisions for the adoption of such alternatives for integrated and sustainable water resource management in semi-arid regions.