Legal Alert

EPA Proposes Strict PFAS Drinking Water Limits

by Harry Weiss and Erin M. Carter
March 15, 2023


The U.S. Environmental Protection Agency is proposing to establish enforceable drinking water limits for six per- and polyfluoroalkyl substances (PFAS): PFOA, PFOS, PFNA, PFHxS, PFBS, and GenX Chemicals.

The Upshot

  • The proposal would regulate PFOA and PFOS as individual contaminants in drinking water, and would regulate PFNA, PFHxS, PFBS, and GenX Chemicals as a mixture in drinking water.
  • The enforceable limit for PFOA (4 ppt) and PFOS (4 ppt) are higher than EPA’s previous established unenforceable health advisories, but lower than any state-level enforceable drinking water standards.
  • Although authority for the rule is the Federal Safe Drinking Water Act (SDWA), under which EPA regulates levels of contaminants acceptable in public water supplies, EPA anticipates publishing a final regulation by the end of 2023 after it receives and reviews public comments and holds a public hearing.

The Bottom Line

The proposed rule would mark the first federal effort to regulate PFAS in drinking water. Several states have already promulgated drinking water standards, all of which are less restrictive than the standards proposed by EPA. If finalized, the new limits would be enforceable nationwide, regardless of previously adopted state-specific PFAS drinking water standards. 

The U.S. Environmental Protection Agency is proposing to establish enforceable drinking water limits for six per- and polyfluoroalkyl substances (PFAS): PFOA, PFOS, PFNA, PFHxS, PFBS, and GenX Chemicals. On March 14, 2023, EPA issued a pre-publication notice of a proposed rule to set drinking water limits for the six PFAS under the SDWA as National Primary Drinking Water Regulations (NPDWR). As expected, the proposed rule sets both health-based non-enforceable Maximum Contaminant Level Goals (MCLGs) and enforceable Maximum Contaminant Levels (MCLs) for drinking water based on the MCLGs. Unlike the purely health-based MCLGs, EPA is required to consider feasibility when promulgating MCLs, such as costs, currently available analytical methods to measure and treat these chemicals, and currently available treatment technologies capable of contaminant removal. As required under the SDWA, EPA has also determined that the benefits of the proposed rule justify the costs, as detailed in EPA’s Health Risk Reduction and Cost Analysis.

Regulation of PFOA and PFOS under the SDWA comes as no surprise. In March 2021, EPA issued a final regulatory determination to regulate PFOA and PFOS as contaminants under the SDWA and in 2022, EPA issued interim health advisories for PFOA, which replaced the EPA’s 2016 health advisories for combined PFOA and PFOS (70 ppt). Note, the 2022 interim health advisories were criticized for being set below detection limits. In yesterday’s proposal, EPA set individual health-based, non-enforceable MCLGs for PFOA and PFOS at zero and enforceable MCLs for PFOA and PFOS at 4ppt. The PFOA and PFOS MCLs exceed the March 2022 interim health advisories, but are lower than any state-level MCL. For example, New Jersey’s MCL for PFOA in drinking water is 14 ppt and 13 ppt for PFOS.

Despite expectations, the proposed scope of the rule caught some by surprise. The regulated community predicted that regulation of perfluorononanoic acid (PFNA), perfluorohexane sulfonic acid (PFHxS), perfluorobutane sulfonic acid (PFBS), and hexafluoropropylene oxide dimer acid and its ammonium salt (GenX Chemicals) would be addressed in some way in this proposed rule, but that enforceable MCLs would be left for another day. Instead, EPA simultaneously proposed (1) a preliminary regulatory determination to regulate these PFAS under the SDWA; (2) a health-based non-enforceable MCGL for mixtures of the chemicals; and (3) an enforceable MCL for mixtures. Note, the MCGL and MCL for these four PFAS is a Hazard Index of 1.0 rather than a limit based on parts per trillion. A Hazard Index is calculated as a sum of hazard quotients (HQ) for PFNA, PFHxS, PFBS, and GenX Chemicals. If the resulting Hazard Index is greater than 1.0, then potential risk is indicated and the MCL would be exceeded.

The proposed rule would also require public water systems to monitor for these six PFAS, and water systems with PFAS levels that exceed the proposed MCLs would be required by the rule to take action to provide safe and reliable drinking water, including by installing water treatment systems, using a new uncontaminated source water, or connecting to an uncontaminated water system.

If finalized, Tuesday’s action will certainly have implications nationwide. Many states have set enforceable drinking water standards for certain PFAS, ranging from 5.1 ppt in California to 667,000 ppt in Nevada—all of which are well above the proposed MCLs for PFOA and PFOS. States with drinking water standards higher than EPA’s proposed MCLs would be preempted by EPA’s regulations and would be required to adopt the NPDWR into state regulations. Even more impactful, some states will have enforceable drinking water standards for any PFAS for the first time.

The proposal would set following drinking water limits for PFOA and PFOS as individual contaminants, while regulating PFNA, PFHxS, PFBS, and GenX Chemicals as a mixture.


Proposed MCLG

Proposed MCL




4.0 parts per trillion (ppt)



4.0 ppt


1.0 Hazard Index

1.0 Hazard Index



HFPO-DA (GenX Chemicals)

Source: EPA, Proposed PFAS National Primary Drinking Water Regulation (March 14, 2023)

The public comment period will open following the proposed rule being published in the Federal Register. Comments may be submitted through the public docket, identified by Docket ID No. EPA-HQ-OW-2022-0114. EPA will be holding a public hearing on May 4, 2023 and EPA anticipates finalizing the regulation by the end of 2023. 

Subscribe to Ballard Spahr Mailing Lists

Get the latest significant legal alerts, news, webinars, and insights that affect your industry. 

Copyright © 2024 by Ballard Spahr LLP.
(No claim to original U.S. government material.)

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, including electronic, mechanical, photocopying, recording, or otherwise, without prior written permission of the author and publisher.

This alert is a periodic publication of Ballard Spahr LLP and is intended to notify recipients of new developments in the law. It should not be construed as legal advice or legal opinion on any specific facts or circumstances. The contents are intended for general informational purposes only, and you are urged to consult your own attorney concerning your situation and specific legal questions you have.