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PFHxS in drinking water

Also called Perfluorohexane sulfonic acid, Perfluorohexanesulfonic acid, Perfluorohexane Sulfonic Acid (PFHxS).

Legal limit
10 ppt
Health goal
10 ppt

Values in parts per trillion (ppt). Comes from the source.

Contaminant referenceLimits checked Oct. 4, 2026

Where the rules stand

Final MCL and health goal of 10 ppt, published April 26, 2024, with compliance due April 26, 2029. PFHxS also counts toward the Hazard Index limit for PFAS mixtures. On May 20, 2026, EPA proposed rescinding the limits for PFHxS, PFNA and HFPO-DA and the Hazard Index. Comments closed July 20, 2026. As of Oct. 4, 2026, the Federal Register shows no final rule, so the 2024 limits still stand.

The scale every TapBuff report uses for this contaminant: the legal line at the middle, twice it at the right.

Is it in your water?

Matched to your utility using EPA records

What EPA says about health

EPA based its 10 ppt health-based level on thyroid effects. When PFHxS occurs with PFNA, HFPO-DA or PFBS, EPA adds their effects together through the Hazard Index.

Where it comes from

PFAS have been used since the 1940s in products like nonstick cookware, food packaging, waterproof clothing, stain-resistant furniture and firefighting foam. They last a long time in the environment and can reach drinking water sources.

What EPA found nationally

Under UCMR 5, EPA tested 9,944 utilities for PFHxS. It was found at 1,015 of them, which report serving 52 million people. The highest single sample was 153 ppt.

Highest single results for PFHxS
UtilityHighest sampleFound in
Bayleaf MasterRaleigh, NC · serves 16,715153 ppt28 of 216
Running Springs Water DistrictRunning Springs, CA · serves 5,26895.5 ppt8 of 22
New MartinsvilleNew Martinsville, WV · serves 5,27284.1 ppt8 of 9
Gwa Northern Water SystemTalofofo, GU · serves 139,20780 ppt80 of 121
Saukville WaterworksSaukville, WI · serves 4,26873 ppt4 of 10
City of TempeTempe, AZ · serves 165,00070.5 ppt8 of 24
Pewaukee City Water and Sewer UtilityPewaukee, WI · serves 8,67169 ppt6 of 16
City of Great BendGreat Bend, KS · serves 14,58060 ppt10 of 20
City of AtwaterAtwater, CA · serves 29,47959 ppt8 of 16
ArtondaleTacoma, WA · serves 5,82855.8 ppt2 of 18
Highest single sample per utility, EPA UCMR 5 file of Aug. 27, 2026. One high sample is not a violation; compliance is judged on averages over time.

What handles it

  • NSF/ANSI 53

    Claim to look for: Total PFAS Reduction

    Same claim, other certifiers’ wording: Perfluorohexane Sulfonic Acid (PFHxS)

    NSF listing footnotes include PFHxS in Total PFAS. NSF says a PFAS claim means reducing PFAS below 20 ppt. EPA says current certifications do not yet show a filter reaches EPA's limits.

    WQA listing wording for a single-compound claim.

NSF’s PFAS claims are tested to below 20 ppt. EPA’s limit is 10 ppt, and EPA says no certification yet shows a filter reaching its levels.

Filters with that claim on a certifier’s listing

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Sources

  1. Per- and Polyfluoroalkyl Substances (PFAS): Final PFAS National Primary Drinking Water Regulation, U.S. EPA. Checked Oct. 4, 2026.
  2. PFAS National Primary Drinking Water Regulation (final rule, April 26, 2024), Federal Register. Checked Oct. 4, 2026.
  3. Rescission of Regulatory Determinations and Removal of Related Provisions for Four PFAS Substances (proposed rule, May 20, 2026), Federal Register. Checked Oct. 4, 2026.
  4. Proposed PFAS Rescission Rule, U.S. EPA. Checked Oct. 4, 2026.
  5. Federal Register: EPA documents mentioning PFAS, newest first (no final rule on either 2026 proposal), Federal Register. Checked Oct. 4, 2026.
  6. The Fifth Unregulated Contaminant Monitoring Rule (UCMR 5) Data Summary: July 2026 (EPA 815-S-26-007), U.S. EPA. Checked Oct. 4, 2026.
  7. NSF listings for the NSF/ANSI 53 "Total PFAS Reduction" claim (footnotes define Total PFAS), NSF. Checked Oct. 4, 2026.
  8. PFAS in Drinking Water, NSF. Checked Oct. 4, 2026.
  9. Fact Sheet: Reducing PFAS in Your Drinking Water with a Home Filter (April 2024), U.S. EPA. Checked Oct. 4, 2026.
  10. Find WQA Certified Products (Gold Seal listings by standard and claim), Water Quality Association. Checked Oct. 4, 2026.
  11. SDWA Dataset Download Summary (codes from SDWA_REF_CODE_VALUES.csv, 2026 Q2 extract), U.S. EPA ECHO. Checked Oct. 4, 2026.