How Drinking Water Standards are Created in California

woman drinking water / photo: istock pablocalvog

The U.S. Environmental Protection Agency establishes federal standards for drinking water contaminants that each state must enforce. These standards determine the maximum concentration allowable for a specific contaminant in drinking water at the tap. States must comply with these standards, but also have the option to adopt more stringent standards, or develop standards regulations for contaminants that the federal government has not acted on (perchlorate is a good example of such a standard). A state cannot set a drinking water standard that is less protective than the US EPA.

In California the State Water Resources Control Board’s Division of Drinking Water (Water Board) is responsible for regulated public water systems that provide drinking water across the State and for establishing drinking water standards for contaminants that threaten our water supply.   Establishing a state drinking water standard for a particular contaminant is a two phase process in California.

Step One:  The California Office of Environmental Health Hazard Assessment (OEHHA) must determine a Public Health Goal (PHG) based on current scientific understanding of the health effects of a particular contaminant.  A PHG is the level of a chemical contaminant in drinking water that does not pose a significant risk to the health of people drinking that water.  For cancer-causing contaminants, OEHHA usually employs a one-in-a million risk level, meaning that exposure to the substance over 70 years would only cause cancer in one person out of a million.

The process by which OEHHA develops a PHG is rigorous.  It involves compiling current scientific studies and evaluating the health risks of the contaminant and developing a draft PHG based upon that information.  Both the evaluation and the proposed PHG are reviewed by a panel of scientific experts (“peer review”).  OEHHA makes revisions based on that peer review, then releases the evaluation and draft PHG for public comment. The comments received – by environmental organizations, public health groups, drinking water providers and industry – may result in further revisions to the PHG.  At this time, any outside party that has concerns about the scientific evaluation performed by OEHHA can request (and must pay for) a second peer review of the PHG.  When all public comments and the 2nd peer review, if applicable, are considered and appropriate revisions made, OEHHA finalizes the PHG.

For more information on PHGs set by OEHHA, please visit this website.

Step Two:  Once OEHHA establishes the PHG for a contaminant, the Water Board must set a legally enforceable drinking water standard.  Drinking water standards are also called Maximum Contaminant Levels (MCLs) because they represent the level of a contaminant in water that public water systems must not exceed. There are two kinds of MCLs; primary MCLs for contaminants that represent a health risk, and secondary MCLs for contaminants that affect the aesthetic quality (taste or physical appearance) of the water.

State law under Health and Safety Code § 116365(a) requires California’s MCLs to be set as close to the PHG as possible, but it also requires that they be based on economic and technical feasibility.  These considerations include monitoring and treatment costs, the ability to detect the contaminant in water, and the effectiveness of treatment technologies.  

Once the Water Board develops a draft MCL for a contaminant, it is reviewed internally by the Department of Finance and Office of Administrative Law.  It then goes through a public comment period before the regulation is finalized and becomes enforceable.  Once the MCL is established, public drinking water providers are legally required to monitor for the contaminant and ensure that levels do not exceed the MCL.

As the primary state regulator of drinking water quality, the Water Board can require drinking water providers to monitor for unregulated contaminants.  The Water Board  may exercise this option, for example, when it is in the process of establishing an MCL and requires more data to determine if the contaminant is a problem or to identify the scope of a new and emerging contaminant problem.

Special Note: MCLs, whether established by the federal government or the State, do not pertain to private drinking water wells – that is, those that serve 1-4 homes. Private well owners are NOT required to test their drinking water for any contaminants.  If you get your drinking water from a private well, we strongly recommend that you contact your local public health agency for guidance on testing your drinking water supply.