Project applicants and agencies alike should think carefully about developing robust analyses that demonstrate the adequacy of water supply.

By Marc T. Campopiano, Diego Enrique Flores, and Lucas I. Quass

Mark Twain is often credited with saying, “Whiskey is for drinking; water is for fighting over.” This remains true in California, where drought conditions, climate change, and population growth throughout the state’s history have made water an increasingly valuable and regulated resource. The legal landscape involves complex questions related to water quality, water sustainability, and competing claims to water rights. One notable area of controversy involves the adequacy of water supply for new development projects.

Two decades ago, in 2001, the state legislature enacted Senate Bill (SB) 610 and SB 221 to promote sustainable long-term water planning. Collectively, SB 610 and SB 221 require public agencies to determine whether adequate water supply exists for certain large development projects as part of the environmental review process under the California Environmental Quality Act (CEQA) by, in part, requesting water supply assessments (WSAs) from water service providers.

Generally, upon request by public agencies, water service providers must prepare WSAs that evaluate whether the projected water supply during normal, single-dry, and multiple-dry water years is sufficient to meet the projected water demand associated with the proposed development project over a 20-year planning horizon. After the water service provider approves the WSA, it is then submitted to the public agency as part of the project’s environmental review under CEQA.

Environmental groups and project opponents have challenged WSAs over the past 20 years, generally focusing on the alleged uncertainty or inadequacy of water supplies.

We reviewed each judicial challenge that has resulted in a California appellate court decision and found that of the 30 Court of Appeal opinions, the WSA and/or the associated environmental review was found to be adequate in 22 cases. Figure 1, below, depicts the counties where these cases were litigated. Notably, roughly two-thirds of the total number of those challenges occurred in Southern California. Challenges to a WSA and a project’s water supply tended to focus on the uncertainty of the water supply, the lack of clarity in the environmental documents, or unanalyzed or unmitigated impacts.

Figure 1

As depicted in Figure 2, below, WSA litigation that ultimately resulted in Court of Appeal decisions tended to originate more often in drought years. Although litigation tends to be driven by case-specific issues, such as opposition to a project by a neighborhood or environmental group, arguments aimed at a project’s water supply may gain more traction when framed within the context of an ongoing drought.

Figure 2


The green dots indicate water supply challenges, while the color shadings indicate the severity of drought. The percentage is the amount of California affected. The National Integrated Drought Information System defines D0 as Abnormally Dry, D1 as Moderate Drought, D2 as Severe Drought, D3 as Extreme Drought, and D4 as Exceptional Drought. For more information, visit

Although agencies typically prevail when WSAs are challenged, project applicants and agencies alike should think carefully about developing robust analyses that demonstrate the adequacy of water supply — especially as California experiences fluctuating periods of droughts.

This article was prepared with the assistance of summer associates Ann Bright and Casey Kirk.