Cost–Benefit Analysis of Onsite Residential Graywater Recycling: A Case Study on the City of Los Angeles

Abstract

A cost–benefit analysis of onsite graywater recycling in single‐family and multifamily homes was conducted to evaluate the merits of graywater recycling in the Los Angeles, Calif., area. Graywater recycling reduces potable water demand by 27 and 38% in single‐family and multifamily homes, respectively. The estimated available graywater is equivalent to 25% of the city's water demand. At a participation level of 10%, Los Angeles will be able to reduce water supply and treatment‐related energy by 43,000 MWh/y, potable water demand by 2%, and wastewater treatment load by 3%. Amending local building codes to require new construction to include plumbing to divert graywater for reuse can lower retrofit costs. Financial tools (e.g., a rebate program, a third‐party ownership model) could lower cost hurdles for graywater recycling. A city‐wide graywater reuse program could be developed to satisfy regulatory requirements by monitoring system operations and maintenance by certified contractors.