Contaminant · PFAS
HFPO-DA (GenX) in drinking water
Hexafluoropropylene oxide dimer acid, the main 'GenX' replacement chemical for PFOA, best known from the Cape Fear River basin.
highest complete sampling-location average; sampled 2023–2025. Source: EPA records; Abbeville City of (Sc0110001) (SC0110001).
What the rules say
The April 2024 PFAS rule set a 10 ng/L (ppt) limit for HFPO-DA (GenX chemicals). In May 2026 EPA proposed rescinding that limit. Until a final decision, the 10 ng/L figure is shown for reference only.
What EPA's assessment says
EPA's 2021 toxicity assessment for GenX chemicals cites liver, kidney, immune and developmental effects in animal studies.
Read the EPA source for HFPO-DA (GenX).
Across the country
EPA tested 10,307 water systems for HFPO-DA (GenX) and found it in 48. Half of the systems that found it measured less than 7.7 ppt, and one in ten measured more than 35.5 ppt.
EPA's final UCMR 5 occurrence file contains 66,362 HFPO-DA (GenX) results from 10,307 systems. 128 results were at or above the minimum reporting level, across 48 systems. Among detections, the median was 7.7 ppt and the 90th percentile was 35.5 ppt.
10 systems had a result at or above the reference on the page's stated comparison basis. For contaminants with a limit, that basis is the yearly average at the highest sampling location, not the highest single sample.
Systems with the highest recorded HFPO-DA (GenX) results
| System | State | Population served | Recorded value | Records / periods |
|---|---|---|---|---|
| Abbeville City of (Sc0110001) SC0110001 | South Carolina | 5,650 | 81.4 ppt | 4 |
| Greenwood Cpw (2410001) SC2410001 | South Carolina | 52,022 | 62.8 ppt | 4 |
| Belton City of (Sc0410004) SC0410004 | South Carolina | 6,762 | 41.9 ppt | 4 |
| Laurens County W&s Comm (Sc3020001) SC3020001 | South Carolina | 44,866 | 35.1 ppt | 5 |
| Robeson County Water System NC0378055 | North Carolina | 67,970 | 33.5 ppt | 2 |
| Honea Path Town of (Sc0410003) SC0410003 | South Carolina | 4,386 | 25.5 ppt | 8 |
| Saluda Cpw (Sc4110001) SC4110001 | South Carolina | 3,390 | 25.2 ppt | 3 |
| Donalds-Due West W&SA (Sc0120001) SC0120001 | South Carolina | 5,200 | 16.4 ppt | 8 |
| Ware Shoals Town of (Sc2410003) SC2410003 | South Carolina | 3,174 | 12.8 ppt | 4 |
| Perth Amboy Water Department NJ1216001 | New Jersey | 52,328 | 11.9 ppt | 4 |
| Newberry City of (3610001) SC3610001 | South Carolina | 9,947 | 8.7 ppt | 4 |
| Bgwc I-20 (Sc3250012) SC3250012 | South Carolina | 7,146 | 8.5 ppt | 4 |
| Joint Municipal WSC (Sc3220003) SC3220003 | South Carolina | 47,838 | 8.3 ppt | 4 |
| Newberry Co W&SA (Sc3620002) SC3620002 | South Carolina | 11,157 | 8.3 ppt | 4 |
| Columbia City of (Sc4010001) SC4010001 | South Carolina | 354,068 | 8.1 ppt | 5 |
| West Columbia City of (Sc3210004) SC3210004 | South Carolina | 34,028 | 7.7 ppt | 8 |
| Lexington Town of (3210001) SC3210001 | South Carolina | 24,284 | 7.2 ppt | 4 |
| Saluda Co W&s Authority (4120001) SC4120001 | South Carolina | 4,535 | 7.1 ppt | 4 |
| The Cape Master System NC0465199 | North Carolina | 11,587 | 7.0 ppt | 2 |
| Goose Creek City of (Sc0810004) SC0810004 | South Carolina | 43,744 | — | 1 |
| Bladen Co Wtr Dist-East Bladen NC0309060 | North Carolina | 4,310 | 6.8 ppt | 1 |
| Amicks Ferry Wtr System (Sc3250077) SC3250077 | South Carolina | 3,937 | 6.6 ppt | 4 |
| Big Sandy Water District KY0100944 | Kentucky | 13,044 | 6.3 ppt | 1 |
| Clinton City of (Sc3010002) SC3010002 | South Carolina | 8,938 | 4.9 ppt | 2 |
| Cayce City of (Sc3210003) SC3210003 | South Carolina | 17,460 | 4.8 ppt | 2 |
Filters and testing
NSF/ANSI 58 (reverse osmosis); carbon filters vary for short-chain PFAS
A standard number by itself is not a contaminant claim. Check the product's current certification listing and performance data sheet for HFPO-DA (GenX) or the specific contaminant you want to reduce. A utility-level record is not a test of your own faucet.