Perchlorate in Drinking Water
EPA has committed to issue a proposed National Primary Drinking Water Regulation for perchlorate by November 21, 2025, and a final regulation by May 21, 2027, as required by court orders. While developing the perchlorate drinking water regulation consistent with the Court mandate, the agency will continue to partner with state co-regulators, Tribes, and communities to address perchlorate in drinking water.
Under the Bipartisan Infrastructure Law, EPA is providing $11.7 billion to the Drinking Water State Revolving Funds, $4 billion to address emerging contaminants, and $5 billion specifically to address emerging contaminants in small or disadvantaged communities, which can all be used to address perchlorate in drinking water. This funding is part of the single-largest investment the U.S. has ever made in water infrastructure and may be used to address perchlorate. EPA also supports research to better understand perchlorate as it relates to firework displays and provides updated technical information to assist drinking water systems and communities that may have concerns about perchlorate contamination of their source water.
On this page:
- Background
- July 2020 Action
- June 2019 Proposed Rule
- Perchlorate Peer Reviews
- Supplemental Information
- Federal Register Notices
Background
Perchlorate is commonly used in solid rocket propellants, munitions, fireworks, airbag initiators for vehicles, matches, and signal flares. Perchlorate may occur naturally, particularly in arid regions such as the southwestern United States and is found as an impurity in hypochlorite solutions used for drinking water treatment and in nitrate salts used to produce nitrate fertilizers, explosives, and other products.
In 2011, EPA issued a determination to regulate perchlorate in drinking water in accordance with the Safe Drinking Water Act (SDWA). EPA delayed proposing a perchlorate regulation in order to complete and allow for peer review of scientific analyses recommended by the agency’s Science Advisory Board. In response to a lawsuit, the U.S. District Court for the Southern District of New York entered a consent decree requiring the EPA to sign a final perchlorate regulation in 2020.
EPA ultimately issued proposed standards for perchlorate in June 2019. In this proposed rule, EPA also requested comment on the withdrawal of its 2011 positive regulatory determination, noting a new health impact analysis indicating that very few public water systems would find perchlorate above a level of health concern. Based on this newer information and analysis presented in the proposed rule, EPA withdrew the 2011 regulatory determination and issued a determination not to regulate perchlorate in July 2020.
In March 2022, EPA announced the completion of its review of the July 2020 perchlorate action pursuant to the requirements of Executive Order 13990. The agency concluded then that the July 2020 action was supported by the best available peer reviewed science and that it was conducted in accordance with the Executive Order. In addition, the agency also announced several measures it was taking to ensure that public health is protected from perchlorate exposure in drinking water. Read EPA’s Press Release & the 2022 Plan to Address Perchlorate Contamination (pdf) (135 K).
In May 2023, the D.C. Circuit vacated and remanded EPA’s July 2020 withdrawal of its determination to issue drinking water regulations for perchlorate. Following this decision, the U.S. District Court for the Southern District of New York ordered the EPA to modify the Consent Decree with new deadlines for EPA to propose and finalize a National Primary Drinking Water Regulation addressing perchlorate.
- May 2023 D.C. Circuit Court Decision (pdf) (315 K)
- Read frequently asked questions about perchlorate in drinking water
July 2020 Action
On July 21, 2020 the U.S. Environmental Protection Agency (EPA) published an action regarding the regulation of perchlorate under the Safe Drinking Water Act (SDWA). Considering the best available science at the time and the proactive steps that EPA, states and public water systems had taken to reduce perchlorate levels, the agency determined that perchlorate did not meet the criteria for regulation as a drinking water contaminant under the SDWA. The agency withdrew the 2011 regulatory determination and made determination to not issue a national regulation for perchlorate.
EPA also performed a new health impact analysis based on recommendations from the Science Advisory Board. The new analysis showed that the concentrations at which perchlorate may present a public health concern were higher than the concentrations considered in the 2011 regulatory determination.
Based on this data and analysis, EPA made a determination that perchlorate was not found in drinking water with a frequency and at levels of public health concern to support a meaningful opportunity for health risk reduction through a national perchlorate drinking water regulation.
In May 2023, the D.C. Circuit vacated and remanded EPA’s July 2020 withdrawal of its determination to issue drinking water regulations for perchlorate.
- May 2023 D.C. Circuit Court Decision (pdf) (315 K)
- Federal Register Notice: Drinking Water: Notice of Final Action on Perchlorate (July 2020)
- Supporting documents are available in Docket ID No. EPA-HQ-OW-2018-0780
- Press Release: EPA Issues Final Action for Perchlorate in Drinking Water (June 2020)
- Fact Sheet: Reductions of Perchlorate in Drinking Water (pdf)
- Fact Sheet: Steps Water Systems Can Take to Address Perchlorate in Drinking Water (pdf)
- Press Release: EPA Notes Successes in Reducing Perchlorate in Drinking Water (May 14, 2020)
June 2019 Proposed Rule
The Environmental Protection Agency (EPA) published a notice of proposed rulemaking in the Federal Register on June 26, 2019 seeking public input on a range of options regarding the regulation of perchlorate in public drinking water systems. The agency requested comment by August 26, 2019 on a proposed National Primary Drinking Water Regulation (NPDWR) for perchlorate to establish a Maximum Contaminant Level (MCL) and a health-based Maximum Contaminant Level Goal (MCLG) at 56 micrograms per liter.
In addition, the agency requested comment on three alternative regulatory options:
- An MCL and MCLG for perchlorate set at 18 micrograms per liter.
- An MCL and MCLG for perchlorate set at 90 micrograms per liter.
- Withdrawal of the agency’s 2011 determination to regulate perchlorate in drinking water.
The agency also requested comment on all relevant aspects of the proposed rule including, but not limited to perchlorate monitoring and reporting requirements for public water systems, a list of treatment technologies that would enable water systems to comply with the MCL, and affordable compliance technologies for small systems serving 10,000 persons or less. EPA also requested comment on its methodology for deriving the MCLG, the underlying assumptions and analysis of its cost and benefit estimates, and other specific items listed in the proposed rule.
Perchlorate is commonly used in solid rocket propellants, munitions, fireworks, airbag initiators for vehicles, matches, and signal flares. Perchlorate may occur naturally, particularly in arid regions such as the southwestern United States and is found as an impurity in hypochlorite solutions used for drinking water treatment and nitrate salts used to produce nitrate fertilizers, explosives, and other products.
- Read the Federal Register Notice
- Additional supporting information is available in Docket ID No. EPA-HQ-OW-2018-0780
Perchlorate Peer Reviews
As part of EPA’s commitment to ensuring the safety of America’s drinking water, the Agency conducted two independent, expert peer reviews to determine the appropriate scientific approach for understanding the adverse health impacts of perchlorate in drinking water.
EPA collaborated with Food and Drug Administration scientists to implement the 2013 Science Advisory Board (SAB) recommendations to develop a Physiologically Based Pharmacokinetic/Pharmacodynamic (PBPK/PD) or Biologically Based Dose Response (BBDR) model that integrated available health related information in a robust and transparent analysis of the effects of perchlorate on thyroid hormone production. A peer review was conducted on the draft model and model report in January 2017. After considering the findings of this review, EPA revised the Perchlorate BBDR Model to focus on increasing the scientific rigor of the model and modeling results. In addition, EPA developed a two-stage approach linking the revised BBDR model results with quantitative information on neurodevelopmental outcomes from epidemiological studies. EPA also developed an alternative population-based approach that uses the revised Perchlorate BBDR Model to evaluate a shift in the population of pregnant women who could be hypothyroxinemic.
Final Peer Review Reports
The final reports for both peer reviews are available through Docket ID No. EPA-HQ-OW-2016-0439.
Supplemental Information
Technical Fact Sheet
Perchlorate Reference Dose
Interim Health Advisory
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Interim Drinking Water Health Advisory for Perchlorate, EPA 822-R-08-25, December 2008
Federal Register Notices
Public Meeting Notices
- Notice of a Public Meeting: Stakeholder Meeting Concerning EPA's Intent To Regulate Perchlorate Levels in Drinking Water - September 20, 2012
- Notification of a Public Meeting and Public Teleconference of the Science Advisory Board: Perchlorate Advisory Panel - July 18-19, 2012 and September 25, 2012
- Notice of a Public Meeting: Environmental Justice Considerations for Drinking Water Regulatory Efforts - March 3, 2011