January 6, 2026
After decades-long resistance, today the U.S. Environmental Protection Agency (EPA) published in the Federal Register proposed drinking water standards for perchlorate. The action comes as a result of a May 2023 decision from the D.C. Circuit Court of Appeals in the case NRDC v. Regan, where the Natural Resources Defense Council (NRDC) sued to compel EPA to issue regulations for perchlorate as required by the Safe Drinking Water Act (SDWA).
Statutory Context
The 1996 amendments to SDWA established a step-wise process in which the EPA must consider unregulated contaminants for potential regulation under SDWA. While the early stages of this process grant EPA considerable discretion, once the agency makes a determination to regulate a contaminant, the statute establishes mandatory requirements and timelines for the agency.
Every five years, the EPA must publish a list of contaminants (Contaminant Candidate List, or CCL) that may warrant SDWA regulation.¹ The agency must make a preliminary determination, subject to notice and comment, whether to regulate at least five CCL contaminants.² After the public comment period for the preliminary determination closes, EPA must issue a final regulatory determination.²
To regulate a contaminant under SDWA, EPA must rely on the best available public health information and find that:
“(i) the contaminant may have an adverse effect on the health of persons;
(ii) the contaminant is known to occur or there is a substantial likelihood that the contaminant will occur in public water systems with a frequency and at levels of public health concern; and
(iii) in the sole judgment of the [EPA] Administrator, regulation of such contaminant presents a meaningful opportunity for health risk reduction for persons served by public water systems.”³
Once the agency determines that the above criteria are met and issues its determination to regulate, the clock starts on the strict regulatory process laid out in the statute. EPA must propose a maximum contaminant level goal (MCLG—unenforceable, health-based value) and a national primary drinking water regulation (NPDWR—enforceable drinking water standard) within 24 months and promulgate a final MCLG and NPDWR within 18 months of the proposal.
Perchlorate Context
Perchlorate is a compound that is both manufactured and naturally-occurring. It is commonly used in solid rocket propellants, munitions, fireworks, vehicle airbag initiators, matches, and signal flares. The defense and aerospace industries are major users of the compound, accounting for 90% of the domestically produced, high grade perchlorate. Consequently, perchlorate is a contaminant of concern at Department of Defense, Department of Energy, and National Aeronautics and Space Administration sites across the country.
Perchlorate toxicity in humans is primarily associated with harmful impacts to the thyroid gland, which is of particular concern for exposed fetuses, infants, and young children. The compound has been detected in drinking water, groundwater, surface water, soil, and sediment. The primary exposure pathway for humans is through ingestion of contaminated food and drinking water.
EPA added perchlorate to the CCL in 1998. The following year, the agency issued its first Unregulated Contaminant Monitoring Rule (UCMR1), requiring large water systems and a sample of small water systems to collect data on the compound between 2001 and 2005.
In 2008, using a health reference level of 15 micrograms/liter (µg/L) and the occurrence data collected under UCMR1, the agency determined that regulation was not warranted for perchlorate under SDWA and issued a preliminary determination not to regulate. After two rounds of public comment, in 2011, EPA issued a final determination to regulate perchlorate in drinking water—a change in course from the preliminary determination. Pursuant to SDWA, the agency was required to propose an MCLG and NPDWR within 24 months of this final determination to regulate, and issue a final MCLG and NPDWR within 18 months of the proposal.
EPA missed these deadlines, and, in 2016, NRDC sued to compel the agency to complete the regulatory process for perchlorate. The parties eventually entered into a consent decree, in which EPA agreed to issue the proposed and final MCLG and NPDWR by 2020. In 2019, EPA issued a rule proposing to set the MCLG and enforceable standard for perchlorate at 56 µg/L, and requesting public comment on that proposal and three alternatives:
1) whether the MCLG and standard should be set at 18 µg/L;
2) whether the MCLG and standard should be set at 90 µg/L; or
3) whether the EPA should withdraw its 2011 determination to regulate based on new information indicating that the occurrence of perchlorate in public water systems does not warrant SDWA regulation.
After receiving public comments on these alternatives, the EPA announced in July 2020 that it was withdrawing its determination to regulate. NRDC again sued the agency, this time challenging the determination not to regulate perchlorate in drinking water.
In May 2023, the D.C. Circuit decided that EPA did not have the authority to withdraw its 2011 determination to regulate, with the majority opinion finding that,
“Because the Safe Drinking Water Act requires that the agency ‘shall’ regulate after making a regulatory determination, EPA lacks authority to withdraw that determination and decide that it ‘shall not’ regulate.”
The Court vacated the agency’s withdrawal of its determination to regulate and remanded to the agency for further proceedings.
In January 2024, EPA committed in a consent decree to issue a proposed MCLG and NPDWR for perchlorate by November 21, 2025, and a final regulation by May 21, 2027. The agency still stands behind its assessment that the best available, peer-reviewed science supports withdrawal of the determination to regulate, and states that the May 2023 Court decision is the only reason it is moving forward with regulating perchlorate under SDWA.
The May 2023 D.C. Circuit decision is telling in how the Court evaluates EPA’s authority to rescind a determination to regulate a contaminant under SDWA—a subject of high importance in the agency’s anticipated actions to walk back its regulation of certain per- and polyfluoroalkyl substances (PFAS, also commonly known as forever chemicals) in drinking water.
Proposed Perchlorate Regulation
The regulation published today proposes an MCLG of 20 µg/L and an enforceable drinking water standard (i.e., maximum contaminant level or MCL) of 20 µg/L, 40 µg/L, or 80 µg/L.
Public comments on the proposed rule are due by March 9, 2026. EPA is holding a virtual public hearing on the rule on February 19, 2026.
Footnotes
1. 42 U.S.C. § 300g-1(b)(1)(B)(i)(I).
2. 42 U.S.C. § 300g-1(b)(1)(B)(ii)(I).
3. 42 U.S.C. § 300g-1(b)(1)(A)(i)–(iii).