Greywater Reuse as a Strategy for Urban Water Transition: Socio-Technical Evidence from an Arid City in Northwest Mexico

Rapid urban growth and increasing water stress in arid regions demand decentralized water management strategies. This study examines the potential for domestic greywater reuse in Mexicali, Mexico, through a multidimensional approach that integrates social perception, water quality, and institutional analysis to evaluate its viability in urban water transition processes. A structured survey was administered to 358 university students to identify consumption patterns and infrastructure using cluster analysis. This was complemented by physicochemical and microbiological characterization of raw greywater from domestic washing machines. Results indicate greywater generation rates of 170–176 L·capita−1·day−1 and high social acceptance of reuse. However, most raw water samples exceeded permissible regulatory limits for organic load and turbidity for non-potable uses, indicating a need for pretreatment. The study concludes that, despite volumetric feasibility and social support, persistent national regulatory gaps and institutional barriers constrain the formal adoption of these technologies. There is an urgent need to develop specific regulations and decentralized adaptive management policies tailored to the realities of arid urban contexts in the Global South.