Arsenic in New Hampshire well water
In New Hampshire, 25% of 18,685 private wells tested between 2006 and 2020 had arsenic above the New Hampshire guidance level (5 ug/L), according to NH DHHS.
Arsenic occurs naturally in New England bedrock and dissolves into well water. Long-term exposure raises the risk of bladder, lung and skin cancers, and is linked to heart disease and lower IQ in children. It has no taste or smell, so testing is the only way to know.
By county, from homeowner tests
Share of private wells above the state guidance level (5 ug/L) in tests homeowners sent to the state lab, 2006 to 2020.
| County | Wells tested | Above state level | Highest | |
|---|---|---|---|---|
| Strafford | 530 | 40% | 183 ug/L | |
| Rockingham | 2,990 | 34% | 766 ug/L | |
| Merrimack | 4,603 | 33% | 1,040 ug/L | |
| Carroll | 1,741 | 26% | 489 ug/L | |
| Hillsborough | 3,558 | 24% | 523 ug/L | |
| Belknap | 1,532 | 22% | 753 ug/L | |
| Sullivan | 627 | 6% | 304 ug/L | |
| Cheshire | 492 | 5% | 34.1 ug/L | |
| Grafton | 2,176 | 5% | 313 ug/L | |
| Coos | 436 | 2% | 29.4 ug/L |
Towns with the highest share above the state level
- Hampton Falls, Rockingham County83% of 36 wells
- Kensington, Rockingham County79% of 34 wells
- Lee, Strafford County66% of 35 wells
- Bow, Merrimack County65% of 689 wells
- Goffstown, Hillsborough County62% of 135 wells
- Pembroke, Merrimack County61% of 113 wells
- Rollinsford, Strafford County60% of 37 wells
- Epping, Rockingham County59% of 44 wells
- South Hampton, Rockingham County58% of 50 wells
- Hancock, Hillsborough County56% of 96 wells
- Dunbarton, Merrimack County56% of 142 wells
- Plaistow, Rockingham County55% of 264 wells
- East Kingston, Rockingham County55% of 33 wells
- Hudson, Hillsborough County53% of 156 wells
- Stratham, Rockingham County50% of 113 wells
- Chichester, Merrimack County48% of 188 wells
- Pelham, Hillsborough County48% of 139 wells
- Francestown, Hillsborough County48% of 46 wells
- Concord, Merrimack County46% of 391 wells
- Durham, Strafford County45% of 73 wells
- Chester, Rockingham County44% of 91 wells
- Brentwood, Rockingham County43% of 51 wells
- Epsom, Merrimack County43% of 146 wells
- Strafford, Strafford County42% of 97 wells
- Madbury, Strafford County42% of 45 wells
By county, from individual samples
Public monitoring samples against the EPA limit (10 ug/L); counties with at least 30 samples.
| County | Samples | Detected | Above EPA limit | Median | Highest |
|---|---|---|---|---|---|
| Rockingham | 322 | 75% | 39% | 4.2 | 150 ug/L |
| Merrimack | 206 | 61% | 25% | 0.65 | 300 ug/L |
| Hillsborough | 225 | 58% | 20% | 1 | 140 ug/L |
| Strafford | 71 | 56% | 4% | 1 | 56 ug/L |
| Sullivan | 32 | 47% | 3% | 0 | 29 ug/L |
| Grafton | 67 | 33% | 1% | 0 | 30 ug/L |
| Carroll | 79 | 20% | 1% | 0 | 160 ug/L |
| Coos | 43 | 21% | 0% | 0 | 6 ug/L |
| Belknap | 32 | 9% | 0% | 0 | 5 ug/L |
Sources
- NH DHHS WISDOM private well summaries: Town summaries of private well tests run by the New Hampshire Public Health Laboratories, published by NH DHHS through the WISDOM environmental public health tracking portal. Exceedance shares use New Hampshire guidance levels, which are stricter than EPA for arsenic (5 ug/L), manganese (0.3 mg/L), radon (2,000 pCi/L) and sodium (20 mg/L). Statistics for small counts are suppressed (*). Retrieved September 3, 2026.
- Individual samples from the USGS Water Quality Portal and state monitoring, summarized per geography. arsenic counts and shares are listed on each county and town page with their sources.