Estimation of residential outdoor water use in Los Angeles, California

The current study analyzes existing methods for estimating outdoor use and landscape irrigation in highly developed residential areas across Los Angeles. Outdoor use was estimated using three methods: two methods described by the Pacific Institute and a third approach that utilizes remotely sensed vegetation and water billing data. Monthly individual water use records were provided by the Los Angeles Department of Water and Power (LADWP) for 2000-2010. This period includes voluntary and mandatory restrictions due to drought conditions across the state. Records were aggregated to the census tract level to protect customer privacy. The two Pacific Institute methods, which are based on water billing data, generally underestimate outdoor use due to assumptions that the lowest water consumption month represents indoor use, which is likely not the case in Los Angeles. The remote-sensing model developed between single-family water use and the Landsat normalized difference vegetation index (NDVI) surplus performed well in greener areas of the city and indicates that landscape irrigation use represents 54% of total single-family water use. The model also predicts an average decrease in landscaping irrigation of 6% and by 35% during voluntary and mandatory restrictions, respectively. Voluntary conservation and mandatory waste restrictions were less effective for higher income groups in the city, while more stringent pricing and non-pricing mandatory restrictions in FY2010 had similar effects across income groups. Study results contribute to a better understanding of the partitioning of Los Angeles residential water use and can be utilized to evaluate pricing structures and target water conservation efforts.