Sustainability Assessment of Decentralized Hybrid Rainwater–Graywater Systems for Water Management in Arid and Semi-Arid Regions: A Systematic Review

Water management in Arid and Semi-Arid Regions (ASAR) relied on large-scale, centralized systems that expanded potable water access. However, high energy requirements, rising operational costs, and limited adaptability to climate variability now put their sustainability under question. According to this study, hybrid rainwater–graywater systems (HRGSs) are emerging as decentralized approaches that can reduce the stress on centralized water systems, increase water supply during dry season, and lower the risk of flooding during rainy seasons. Identifying and evaluating a comprehensive sustainability framework of HRGSs for ASARs remains underexplored. To address this gap, a systematic review of literature indexed in two databases, Scopus and Engineering Village, was performed. Forty studies met the inclusion criteria and were critically appraised to delineate their scope, recurring patterns, and frameworks. Moreover, this study developed a comprehensive sustainability framework specific to the ASAR context, proposing key indicators for HRGS evaluation across environmental, economic, and social aspects with their indicators. Proposing a new sustainability framework provides a basis for guiding future research, technology design, and policy development aimed at implementing HRGS in ASAR contexts.