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HFPO-DA (GenX) in drinking water

Also called GenX, GenX chemicals, Hexafluoropropylene oxide dimer acid.

Legal limit
10 ppt
Health goal
10 ppt

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

Where the rules stand

Final MCL and health goal of 10 ppt, published April 26, 2024, with compliance due April 26, 2029. HFPO-DA 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. No NSF or WQA listing shows a reduction claim for HFPO-DA, and it is not in NSF's Total PFAS claim.

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

What EPA says about health

EPA based its 10 ppt health-based level on liver effects. When HFPO-DA occurs with PFHxS, PFNA 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 HFPO-DA (GenX). It was found at 47 of them, which report serving 1.8 million people. The highest single sample was 170 ppt.

Highest single results for HFPO-DA (GenX)
UtilityHighest sampleFound in
City of AbbevilleAbbeville, SC · serves 5,650170 ppt4 of 4
Laurens County W&S CommLaurens, SC · serves 44,86695.8 ppt5 of 12
Greenwood CpwGreenwood, SC · serves 52,02291.1 ppt4 of 4
City of BeltonBelton, SC · serves 6,76282.9 ppt4 of 4
Saluda CpwSaluda, SC · serves 3,39043 ppt3 of 4
Town of Honea PathHonea Path, SC · serves 4,38642 ppt8 of 8
Donalds - Due West W&SADonalds, SC · serves 5,20040 ppt8 of 8
Robeson County Water SystemMaxton, NC · serves 67,97034 ppt2 of 24
Big Sandy Water DistrictCatlettsburg, KY · serves 13,04425 ppt1 of 16
Town of Ware ShoalsWare Shoals, SC · serves 3,17422 ppt4 of 4
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

No NSF/ANSI reduction claim exists for HFPO-DA (GenX), so no filter can be certified to remove it. Be wary of any product that says otherwise.

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. Search for NSF Certified Drinking Water Treatment Units (standards and reduction claims lists), NSF. Checked Oct. 4, 2026.
  8. NSF listings for the NSF/ANSI 53 "Total PFAS Reduction" claim (footnotes define Total PFAS), NSF. Checked Oct. 4, 2026.
  9. Find WQA Certified Products (Gold Seal listings by standard and claim), Water Quality Association. Checked Oct. 4, 2026.
  10. SDWA Dataset Download Summary (codes from SDWA_REF_CODE_VALUES.csv, 2026 Q2 extract), U.S. EPA ECHO. Checked Oct. 4, 2026.