Six-Year Review 4 of Drinking Water Standards
On this page:
- Overview
- Results Summary
- Federal Register Notice and Frequent Questions
- Support Documents and Occurrence Data for EPA's Fourth Review of Existing Drinking Water Standards
- Information Collection Request
Overview
In July 2024, EPA announced the results of the fourth cycle of its Six-Year Review of existing national primary drinking water regulations (NPDWRs). Based on the agency's review of existing NPDWRs, EPA determined that there are no additional candidates identified for regulatory revision.
The Safe Drinking Water Act (SDWA) requires the EPA to conduct a review every six years of existing NPDWRs and determine which, if any, are appropriate for revision. The purpose of the review is to evaluate available information for regulated contaminants to determine if any new information on health effects, treatment technologies, analytical methods, occurrence, exposure, implementation, and/or other factors provides a basis to support a regulatory revision that would improve or strengthen public health protection.
The Six-Year Review is not a final regulatory decision to revise or not revise an NPDWR, but rather the initiation of a planning process that involves more detailed analyses of factors relevant to deciding whether a rulemaking effort to revise an NPDWR should be considered.
For NPDWRs not identified as a candidate for revision, it means that the agency has concluded that it is not appropriate for revision at the time based on available information. The criteria that EPA has applied to help identify when an NPDWR might be considered as a “candidate for revision” are, at a minimum, that the regulatory revision presents a meaningful opportunity to improve the level of public health protection, and/or achieve cost savings while maintaining or improving the level of public health protection.
EPA did not include in this Six-Year Review cycle the recently promulgated per-and polyfluoroalkyl substances (PFAS) regulations. The PFAS regulations, promulgated in April 2024, established six new NPDWRs. The EPA anticipates that once the PFAS regulations go into effect and sufficient information regarding compliance monitoring becomes available, those NPDWRs will be subject to a more detailed regulatory review under a future Six-Year Review cycle.
Summary of Six-Year Review 4 Results
Learn more about the drinking water contaminants listed below
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Summary of Review Outcomes |
Regulated Contaminants |
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Not Appropriate for Revision at this Time. |
Recently completed, ongoing or pending regulatory action. |
Bromate |
Haloacetic acids (HAA5) |
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Chloramines (as Cl2) |
Heterotrophic bacteria |
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Chlorine Dioxide (as ClO2) |
Lead |
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Chlorine (as Cl2) |
Legionella |
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Chlorite |
Total Trihalomethanes (TTHM) |
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Copper |
Turbidity |
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Cryptosporidium (IE, LT1) 1 |
Viruses (SWTR, IE, LT1) 1 |
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Giardia lamblia |
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Not Appropriate for Revision at this Time. |
Health effects assessment in process or contaminant nominated for health assessment. |
Alpha/photon emitters |
Mercury (inorganic) |
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Arsenic |
Polychlorinated biphenyls (PCBs) |
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Beta/photon emitters |
Radium 226/228 (combined) |
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Chromium (total) |
Uranium |
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Ethylbenzene |
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No new information, NPDWR remains appropriate after review. |
Asbestos |
trans-1,2-Dichloroethylene |
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Benzo(a)pyrene |
Dinoseb |
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Chlorobenzene |
E. coli |
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Dalapon |
Endrin |
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Di(2-ethylhexyl)adipate (DEHA) |
Ethylene dibromide |
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Di(2-ethylhexyl)phthalate (DEHP) |
2,4,5-TP (Silvex) |
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1,2-Dibromo-3-chloropropane (DBCP) |
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New information, but no revision recommended because… |
Low priority and/or no meaningful opportunity |
Acrylamide |
Heptachlor |
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Alachlor |
Heptachlor Epoxide |
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Antimony |
Hexachlorobenzene |
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Atrazine |
Hexachlorocyclopentadiene |
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Barium |
Lindane |
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Benzene |
Methoxychlor |
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Beryllium |
Oxamyl (Vydate) |
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Cadmium |
Pentachlorophenol |
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Carbofuran |
Picloram |
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Carbon Tetrachloride |
Selenium |
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Chlordane |
Simazine |
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Cryptosporidium (LT2) 1 |
Styrene |
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1,2-Dichlorobenzene |
Tetrachloroethylene (PCE) |
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1,4-Dichlorobenzene |
Thallium |
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1,2-Dichloroethane |
1,2,4-Trichlorobenzene |
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1,1-Dichloroethylene |
1,1,1-Trichloroethane |
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cis-1,2-Dichloroethylene |
1,1,2-Trichloroethane |
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Dichloromethane |
Toluene |
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2,4-Dichlorophenoxyacetic acid (2,4-D) |
Total Coliform |
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1,2-Dichoropropane |
Toxaphene |
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Dioxin (2,3,7,8-TCDD) |
Trichloroethylene (TCE) |
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Diquat |
Vinyl Chloride |
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Endothall |
Xylenes |
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Epichlorohydrin |
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Glyphosate |
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Emerging information and/or data gaps |
Cyanide (as free cyanide) |
Nitrate |
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Fluoride |
Nitrite |
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Candidate for Revision |
New information |
None |
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- Regulation abbreviations: Aircraft Drinking Water Rule (ADWR), Ground Water Rule (GWR), Revised Total Coliform Rule (RTCR), Surface Water Treatment Rule (SWTR), Interim Enhanced Surface Water Treatment Rule (IE), Long Term 1 Enhanced Surface Water Treatment Rule (LT1), and Long Term 2 Enhanced Surface Water Treatment Rule (LT2).
Federal Register Notice and Frequent Questions About Six-Year Review 4
- Federal Register Notice: Six-Year Review 4
- Read Frequent Questions and Answers for Six-Year Review 4