Abstract This study evaluates an integrated greywater reuse and rooftop solar photovoltaic (PV) concept for a luxury residential compound in New Cairo, Egypt (365 buildings; 7,512 units). Based on stated per‑capita end‑use assumptions, total greywater production is 6,300 m 3 /day (2,299,500 m 3 /year), while toilet flushing demand is 2,700 m 3 /day (985,500 m 3 /year). A physico‑chemical onsite treatment train (coagulation, multimedia filtration, chlorination) is specified at 6,300 m 3 /day; using a 5% filter backwash assumption, annual hydraulic recovery is 95% (2,184,525 m 3 /year). The recovered volume exceeds the flushing demand, indicating demand‑limited potable‑water offset for the quantified end use and potential surplus for additional non‑potable applications. The greywater system CAPEX is 3.37 million USD (535 USD/(m 3 /day)) with disaggregated components for in‑building supply, transfer networks, and the treatment plant. Total OPEX is 0.06 USD/m 3 (137,970 USD/year at design flow), yielding a straight‑line levelized cost of water (LCOW) of 0.133 USD/m 3 on a treated‑volume basis and 0.311 USD/m 3 on a potable‑offset basis over the 20‑year analysis horizon. For the PV system, the total initial cost for 365 buildings is 666,455,000 EGP, with modeled annual electricity cost savings of 5,348,550 EGP and an indicative simple payback of approximately 10 years. Overall, the results quantify the magnitude of potable‑water offset and cost metrics achievable at compound scale.
Abdo et al. (Wed,) studied this question.