PFHxS in well water
PFHxS comes mainly from firefighting foam and persists in the body longer than most PFAS. It is linked to thyroid and immune effects. Wells near airports, fire stations and training grounds are most at risk.
- EPA limit
- 10 ng/L (EPA MCL (2024 PFAS rule; proposed for rescission May 2026); New Hampshire MCL is 18 ng/L)
- CAS number
- 355-46-4
By individual samples
Counties with at least 30 individual samples in public monitoring data, against the EPA limit.
| County | Samples | Detected | Above EPA limit | Median |
|---|---|---|---|---|
| Washington County, Maine | 36 | 25% | 6% | 0 ng/L |
| Franklin County, Maine | 44 | 16% | 5% | 0 ng/L |
| Somerset County, Maine | 575 | 36% | 2% | 0 ng/L |
| Oxford County, Maine | 72 | 18% | 1% | 0 ng/L |
| Penobscot County, Maine | 294 | 26% | 1% | 0 ng/L |
| Sagadahoc County, Maine | 170 | 22% | 1% | 0 ng/L |
| York County, Maine | 385 | 36% | 1% | 0 ng/L |
| Lincoln County, Maine | 110 | 35% | <1% | 0 ng/L |
| Aroostook County, Maine | 113 | 23% | <1% | 0 ng/L |
| Hillsborough County, New Hampshire | 3,793 | 82% | <1% | 0.79 ng/L |
| Waldo County, Maine | 401 | 18% | <1% | 0 ng/L |
| Cumberland County, Maine | 573 | 43% | <1% | 0 ng/L |
| Kennebec County, Maine | 450 | 27% | <1% | 0 ng/L |
| Strafford County, New Hampshire | 157 | 57% | <1% | 0.21 ng/L |
| Rockingham County, New Hampshire | 2,122 | 81% | <1% | 0.87 ng/L |
How to test
Use a state-certified lab and a proper sampling bottle; hardware-store strips cannot measure pfhxs at the levels that matter. Collect from the kitchen tap before any treatment, and again after treatment if you install it.
How to treat
- Granular activated carbon whole-house
- Point-of-use reverse osmosis
- Anion exchange