Fluoride in well water
The county where Fluoride is found above the limit most often is Hancock County, Maine: 6% of 2,937 private wells tested, according to Maine Tracking Network private well summaries.
Natural fluoride in bedrock wells can exceed the limit. Above 4 mg/L long-term exposure causes skeletal fluorosis; above 2 mg/L children can develop tooth mottling.
- EPA limit
- 4 mg/L (EPA MCL (40 CFR 141.62))
- Nuisance level
- 2 mg/L
- New Hampshire level
- 2 mg/L
- CAS number
- 16984-48-8
Where fluoride is worst, by homeowner tests
Counties ranked by the share of private wells above the state guidance level in tests homeowners sent to the state lab. Shares combine town summaries, weighted by wells tested.
| County | Wells tested | Above state level | Highest | |
|---|---|---|---|---|
| Hancock County, Maine | 2,937 | 6% | ||
| Oxford County, Maine | 1,468 | 4% | ||
| Franklin County, Maine | 899 | 4% | ||
| Carroll County, New Hampshire | 1,910 | 4% | 15 mg/L | |
| York County, Maine | 2,695 | 3% | ||
| Kennebec County, Maine | 5,015 | 2% | ||
| Somerset County, Maine | 1,078 | 2% | ||
| Cumberland County, Maine | 4,655 | 2% | ||
| Androscoggin County, Maine | 1,582 | 2% | ||
| Washington County, Maine | 1,443 | 2% | ||
| Waldo County, Maine | 1,664 | 2% | ||
| Lincoln County, Maine | 1,981 | 1% | ||
| Grafton County, New Hampshire | 2,594 | <1% | 11 mg/L | |
| Sagadahoc County, Maine | 1,246 | <1% | ||
| Knox County, Maine | 819 | <1% |
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 |
|---|---|---|---|---|
| Carroll County, New Hampshire | 210 | 90% | 11% | 1.2 mg/L |
| Coos County, New Hampshire | 173 | 76% | 1% | 0.2 mg/L |
| Belknap County, New Hampshire | 186 | 90% | 1% | 0.4 mg/L |
| Merrimack County, New Hampshire | 497 | 85% | 1% | 0.3 mg/L |
| Hillsborough County, New Hampshire | 177 | 79% | <1% | 0.2 mg/L |
| Rockingham County, New Hampshire | 332 | 79% | <1% | 0.07 mg/L |
| Cheshire County, New Hampshire | 68 | 90% | 0% | 0.2 mg/L |
| Grafton County, New Hampshire | 240 | 75% | 0% | 0.2 mg/L |
| Sullivan County, New Hampshire | 48 | 75% | 0% | 0.1 mg/L |
| Strafford County, New Hampshire | 94 | 66% | 0% | 0.1 mg/L |
How to test
Use a state-certified lab and a proper sampling bottle; hardware-store strips cannot measure fluoride at the levels that matter. Collect from the kitchen tap before any treatment, and again after treatment if you install it.
How to treat
- Point-of-use reverse osmosis
- Activated alumina
- Distillation