Drinking Water Health Advisories (HAs) | US EPA – U.S. EPA.gov

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The Safe Drinking Water Act (SDWA) authorizes EPA to issue HAs for contaminants that are not subject to a National Primary Drinking Water Regulation (NPDWR) (42 U.S.C. §300g-1(b)(1)(F)). HA documents provide technical information on chemical and microbial contaminants that can cause human health effects and are known or anticipated to occur in drinking water. HA values/levels identify the concentration of a contaminant in drinking water at which adverse health effects and/or aesthetic effects are not anticipated to occur over specific exposure durations (e.g., 1 day, 10 days, a lifetime). HAs primarily serve as information to drinking water systems and officials responsible for protecting public health when emergency spills or other contamination situations occur. They help Tribes, states, and local governments inform the public and determine whether local actions are needed to address public health impacts in affected communities. EPA’s HA documents describe information about health effects, analytical methodologies, and treatment technologies. HAs are not to be construed as legally enforceable federal standards and are subject to change as new information becomes available.
EPA can develop interim or provisional HA levels to provide information in response to an urgent or rapidly developing situation. Interim or provisional HAs are also based on health-based hazard concentrations above which action should be taken to reduce exposure to unregulated contaminants in drinking water. They can be updated or removed as additional information becomes available. For example, EPA published provisional HAs for PFOA and PFOS in 2009 and interim updated HAs for PFOA and PFOS in 2022.
EPA’s Drinking Water Standards and Health Advisories tables contain HA levels for approximately 200 contaminants based on non-cancer health effects for different durations of exposure (e.g., one-day, ten-day, and lifetime) as well as the underlying reference dose (RfD) supporting the lifetime HAs or, if applicable, the cancer risk values for drinking water contaminants. The tables also include the contaminants currently regulated under SDWA for which EPA has established Maximum Contaminant Level Goals (MCLGs) as well as Maximum Contaminant Levels (MCLs; also known as drinking water standards). An MCLG is the level of a contaminant in drinking water below which there is no known or expected risk to health. MCLGs allow for a margin of safety and are non-enforceable public health goals. An MCL is the highest level of a contaminant that is allowed in drinking water. MCLs are set as close to MCLGs as feasible using the best available treatment technology and taking cost into consideration. MCLs are enforceable standards.
As stated in EPA’s PFAS Strategic Roadmap, PFAS contamination has impacted drinking water quality across the country, including in underserved rural areas and communities of color. Going forward, EPA anticipates developing HAs for additional PFAS or categories of PFAS as the Agency publishes toxicity assessments.

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