Fluoride in Maine well water
In Maine, 2% of 31,960 private wells tested had fluoride above the Maine guideline (2 mg/L), according to Maine CDC.
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.
By county, from homeowner tests
Share of private wells above the state guidance level (2 mg/L) in tests homeowners sent to the state lab, to .
| County | Wells tested | Above state level | Highest | |
|---|---|---|---|---|
| Hancock | 2,937 | 6% | ||
| Oxford | 1,468 | 4% | ||
| Franklin | 899 | 4% | ||
| York | 2,695 | 3% | ||
| Kennebec | 5,015 | 2% | ||
| Somerset | 1,078 | 2% | ||
| Cumberland | 4,655 | 2% | ||
| Androscoggin | 1,582 | 2% | ||
| Washington | 1,443 | 2% | ||
| Waldo | 1,664 | 2% | ||
| Lincoln | 1,981 | 1% | ||
| Sagadahoc | 1,246 | <1% | ||
| Knox | 819 | <1% | ||
| Penobscot | 3,177 | <1% | ||
| Aroostook | 951 | 0% |
Towns with the highest share above the state level
- Otis, Hancock County32% of 44 wells
- Dedham, Hancock County19% of 79 wells
- Marshfield, Washington County18% of 33 wells
- Surry, Hancock County18% of 146 wells
- Prospect, Waldo County16% of 61 wells
- Fryeburg, Oxford County16% of 50 wells
- Denmark, Oxford County16% of 45 wells
- Kennebunk, York County15% of 92 wells
- Sedgwick, Hancock County15% of 87 wells
- Mariaville, Hancock County14% of 35 wells
- Smithfield, Somerset County13% of 40 wells
- Mechanic Falls, Androscoggin County13% of 32 wells
- Porter, Oxford County12% of 34 wells
- Stockton Springs, Waldo County11% of 36 wells
- Norridgewock, Somerset County11% of 93 wells
- Brownfield, Oxford County11% of 37 wells
- Raymond, Cumberland County10% of 212 wells
- Otisfield, Oxford County9% of 69 wells
- Casco, Cumberland County9% of 151 wells
- Chesterville, Franklin County9% of 93 wells
- Hiram, Oxford County9% of 59 wells
- York, York County8% of 119 wells
- Blue Hill, Hancock County8% of 157 wells
- Biddeford, York County8% of 75 wells
- Ellsworth, Hancock County8% of 431 wells
Sources
- Maine Tracking Network private well summaries: Town summaries of private well tests run by the Maine Health and Environmental Testing Laboratory, published by Maine CDC through the Maine Tracking Network. Shares are against Maine's guideline for each analyte (arsenic 10 ug/L, uranium 30 ug/L, fluoride 2 mg/L, manganese 0.3 mg/L, nitrate 10 mg/L, nitrite 1 mg/L). Towns with too few tests are suppressed (NR). Only the share above the guideline and wells tested are published; no medians. Retrieved September 3, 2026.
- Individual samples from the USGS Water Quality Portal and state monitoring, summarized per geography. fluoride counts and shares are listed on each county and town page with their sources.