EPA Finalizes Drinking Water Standards for Six PFAS

On April 10, 2024, the US EPA announced the final National Primary Drinking Water Regulations (NPDWR) for six Per- and Polyfluoroalkyl Substances (PFAS). The maximum contaminant levels (MCL) for the six PFAS in drinking water are shown below. An MCL is an enforceable legal standard that identifies the highest level of a contaminant that is allowed in public drinking water.

US EPA drinking water maximum contaminant levels (MCL) for PFAS

As an additional layer of protection, a hazard index MCL of 1 (unitless) will be used to limit exposure to mixtures containing at least two of the following: PFNA, HFPO-DA, PFHxS, and PFBS. While different from a typical MCL, this Hazard Index considers the different toxicities of PFNA, GenX chemicals, PFHxS, and PFBS and determines if the combined levels of these PFAS in the drinking water pose a potential risk and require action. The Hazard Index (PDF) is calculated by dividing the measured concentration in drinking water by a corresponding health-based concentration of the chemical determined not to have a risk of human health effects for each of the four compounds. A total value greater than one would indicate an exceedance of the Hazard Index MCL of 1.

The final MCLs are enforceable federal drinking water standards that will require public water systems to reduce levels of the six PFAS in finished water.  Public water systems are those that regularly provide drinking water to at least 25 individuals. These public water systems will have until 2029 (5 years) to monitor their treated water and implement treatment solutions to lower PFAS levels in finished water if levels exceed the final MCLs. These MCLs do not apply to drinking water from private water systems such as private wells, springs, or cisterns. 

For additional information about drinking water regulations and the final PFAS regulations in drinking water visit:

• How EPA Regulates Drinking Water Contaminants
• Per- and Polyfluoroalkyl Substances (PFAS) Final PFAS National Primary Drinking Water Regulation