Well water by county: Massachusetts
Across 12 counties in Massachusetts, 34 of 472 sampled wells (7%) were above the arsenic limit and 106 of 2554 (4%) above the nitrate limit. Updated 2026-10-18. Source: Water Quality Portal (USGS, EPA, NWQMC), siteType=Well.
Share of sampled wells whose latest result is above the EPA limit (arsenic 10 µg/L, nitrate 10 mg/L as N).
| County | Arsenic > 10 µg/L | Nitrate > 10 mg/L |
|---|---|---|
| Barnstable County | 2% of 123 | 5% of 1,705 |
| Berkshire County | 0% of 10 | 0% of 108 |
| Bristol County | 0% of 18 | 4% of 25 |
| Essex County | 0% of 13 | 3% of 70 |
| Franklin County | – | 4% of 53 |
| Hampden County | 4% of 24 | 4% of 69 |
| Hampshire County | 0% of 17 | 0% of 24 |
| Middlesex County | 3% of 29 | 6% of 156 |
| Nantucket County | – | 7% of 14 |
| Norfolk County | 3% of 33 | 0% of 73 |
| Plymouth County | 0% of 75 | 2% of 131 |
| Worcester County | 22% of 130 | 1% of 126 |