Drinking Water Quality in an Evolving World

January 2021


From the source to the tap, ensuring water quality is of paramount importance to the well-being of California’s environment, economy and residents. For drinking water, there is a robust regulatory structure that governs the implementation of the state and federal Safe Drinking Water Acts.

Drinking Water Standards

The State Water Resources Control Board’s Division of Drinking Water (DDW) is responsible for regulating drinking water in California. These efforts are informed by risk assessments and Public Heath Goals established by the Office of Environmental Health Hazard Assessment (OEHHA). There are several steps in developing a drinking water standard: Notification and Response Levels, Public Health Goal, and Maximum Contaminant Level.

Notification and Response Levels (NLs/RLs). NLs/RLs are non-enforceable, health-based advisory levels, although there are certain notification requirements to customers if a water source exceeds these levels. DDW recommends the source be taken out of service if it exceeds the response level. AB 2560 (2020), sponsored by CMUA and Orange County Water District, enhanced the notification and public participation requirements for establishing these levels.

Public Health Goal (PHG). The PHG is based exclusively on public health considerations and is not meant to be an enforceable standard. Water systems must publish information about PHGs in their Consumer Confidence Reports, which are distributed annually to customers.

Maximum Contaminant Level (MCL). Also called a drinking water standard, the MCL is the final step in the regulatory process and it is the only enforceable level. When determining the MCL, DDW reviews the PHG, any MCL or MCL goal developed by U.S. Environmental Protection Agency, and the technological and economic feasibility of complying with the MCL. The law requires that DDW set the MCL as close as possible to the PHG, taking into account the other factors.

Constituents of Emerging Concern

For various reasons, including advances in detection and health effects research, California continues to confront a series of Constituents of Emerging Concern (CECs) in the drinking water supply. CECs are a diverse group of chemicals and microorganisms that have been detected in drinking water at trace levels and for which the risk to human health or the environment is not yet fully known. Pharmaceuticals, personal care products (PCPs) and algal toxins are among examples of CECs that are of growing concern. In the past, hexavalent chromium, perchlorate, arsenic and lead were identified this way.

The federal process to identify and collect data on CECs relies upon the Contaminant Candidate List and the Unregulated Contaminant Monitoring Rule, which can take several years before a final regulatory decision is made and may not focus on issues specific to California. There currently is no coordinated effort in our state to address CECs in drinking water.

Because CECs are complex and our understanding continues to evolve, the State Water Board should have a comprehensive program, including a Science Advisory Panel, to systematically review, evaluate and assist Board members and staff as they address CECs in drinking water. While legislative approaches can address public concerns, bills can be passed without complete information on occurrence and health effects. A comprehensive program would enable the state to proactively and more quickly research and establish NLs/RLs, PHGs and MCLs based on sufficient, robust and peer-reviewed science. CMUA and Metropolitan Water District of Southern California are co-sponsoring legislation in 2021 to establish such a program.

The state of California also should develop robust communication tools that help the public understand what is often a complicated issue and encourage business to find better alternatives for the environment and public health.