How Effective Are Building Codes at Reducing Residential Water Use? Evidence from California Billing Data

• In Event: Water Policy Under Pressure: Interdisciplinary Insights for Resilient Governance

Abstract

Per capita water use has been declining partly because water utilities continue to put significant effort into increasing water use efficiency, particularly in the residential sector. A recent report finds that nationwide residential water use, measured in gallons per capita per day (GPCD), decreased from 101 GPCD in 1995 to 82 GPCD in 2015 (1). Notably, California has achieved significant reductions in per capita residential water use, which decreased by 34% between 1994 and 2019 (2, 3). These reductions are attributed to various state- and local-level demand-side management policies, such as the introduction of new technologies to increase water use efficiency, conservation pricing, rebates, and regulations, including water quotas and use bans (4-10). One demand-side residential water policy gaining attention nationwide and globally, though its ex-post effectiveness has not been extensively studied, is the use of building and plumbing codes to increase water use efficiency.

Empirical evidence on the actual impact of building regulations is limited, with the primary focus being household energy consumption (electricity and gas).

While energy consumption has been the primary focus of building efficiency programs (18-21, 23, 24), water efficiency has become a more prominent component of green building standards and building codes (25). Building codes for water efficiency were first introduced in California in 2010, the California Green Building Standards Code, also known as CALGreen, and have since been adopted in various states.  Although a few studies quantify the ex-ante effectiveness of building code requirements (27), there is, to our knowledge, no comprehensive analysis of their ex-post impacts. It is especially important to quantify these impacts as more states adopt such requirements and those with existing building codes continue to enhance them or add more stringent requirements. This paper addresses this gap by evaluating the ex-post effectiveness of these building codes using household-level billing data.

Similar to previous studies in the energy sector (18, 19, 21), this paper leverages utility billing data to directly compare the water consumption of households built under CALGreen requirements with those constructed just before the code's implementation. This paper makes several contributions by being the first to use residential billing data to evaluate both the short- and long-term effects of building codes on water consumption and expenditure. Additionally, it compares these ex-post estimates to the ex-ante estimates provided in CALGreen. Further, we investigate the heterogeneity in the impact of CALGreen by season and temperature levels.

The results show that, on average, homes built after the implementation of CALGreen experience an approximately 12% reduction in water demand in the short term. These reductions persist over time, with a sustained long-term reduction of around 11%. However, these effects are about half of the ex-ante estimates of CALGreen's impact. The study also reveals that the majority of water savings occur during the warmer months when lawn irrigation is at its peak. Additionally, homes built under CALGreen standards exhibit lower sensitivity to temperature fluctuations, showing smaller increases in water use during hotter months and smaller reductions in water use during cool months.

Author

• Mehdi Nemati, University of California, Riverside
  Presenting Author