Treated greywater reuse for sustainable landscape irrigation in cities with water scarcity

Abstract Treated greywater offers a practical alternative to potable water for non-food landscape irrigation when treatment and monitoring are matched to source composition and exposure. Because the reviewed studies differed in design, scale, climate and monitoring, performance was synthesized as reported ranges rather than pooled averages. Bathroom-only greywater can often be managed through source control, filtration and restricted subsurface irrigation. Laundry-inclusive streams additionally require sodium, boron and surfactant control, whereas kitchen-inclusive or mixed streams need grease interception, stronger pretreatment and biological or physicochemical barriers. Public-access landscapes require validated disinfection, process verification and cross-connection protection. Membrane systems provide compact treatment with consistently high solids removal and strong microbial control but require more energy, fouling management and operator skills. Nature-based systems can lower energy and operational demands where land is available but require hydraulic stability and final microbial safeguards. Long-term evidence remains limited for the accumulation of pharmaceuticals, personal-care products, microplastics, persistent detergent residues and antimicrobial-resistant organisms in arid soils and groundwater. Egypt regulates the irrigation use of treated municipal wastewater but lacks a national framework for building-scale greywater reuse. Priorities include a greywater-specific approval pathway, clear institutional responsibility, multi-season pilots and long-term soil, groundwater and operational monitoring. Treated greywater is therefore a practical circular resource only when water savings are balanced against health, soil, energy and management risks. No meta-analysis or formal life-cycle assessment was conducted.