The effectiveness of water conservation measures on summer residential water use in Los Angeles, California

• Water restriction policies are analyzed for efficacy across Los Angeles, CA.
• Ten years of monthly water billing data from LA Department of Water and Power utilized.
• Predictive statistical model developed with water, climate and unemployment data.
• Voluntary restrictions not effective in reducing water use.
• Most progressive restrictions resulted in average of 23% decrease in water use across the City.

Warmer and drier conditions over the past decade in California, in addition to court-mandated restrictions on the Sacramento River Delta water supply, have generally reduced the amount of water resources available to Southern California. These constraints on water supply led water agencies to implement a range of water conservation and watering restrictions programs, mostly targeted at outdoor use. The City of Los Angeles, the largest of 88 cities in the County of Los Angeles and the most populous in the United States, took several measures to attempt to reduce residential water consumption. Three phases of water restrictions were implemented during the 2008–2010 period: voluntary restrictions (FY2008), mandatory restrictions (FY2009), and yet more stringent mandatory restrictions combined with a price increase and a decrease in overall household allocations (FY2010). Our research aims at quantifying the impact of these increasing restrictions on single-family residential water use across the City. Ten years of monthly individual billing data (2000–2010) were obtained from the Los Angeles Department of Water and Power (LADWP), the municipal utility for the City. Monthly single-family customer water use records at the Public Use Microdata Area level from 2000 to 2007 were used to develop and validate a linear regression model that integrated unemployment and climate information during a period without restrictions. Predictions from the model were then compared to actual consumption to assess the impact of water restrictions during the 2008–2010 period. We also contrasted voluntary water restrictions counseled by LADWP with mandatory water use restrictions. Results show that more stringent mandatory outdoor watering restrictions combined with pricing measures were most effective and resulted in a 23% decrease in City average single-family water use during summer of FY2010. Voluntary restrictions in FY2008 were less effective in reducing water use.