Manganese in New Hampshire well water
In New Hampshire, 6% of 17,431 private wells tested between 2006 and 2020 had manganese above the New Hampshire guidance level (300 ug/L), according to NH DHHS.
Manganese stains fixtures and laundry above 50 ug/L. EPA's health advisory is 300 ug/L; infants are the most sensitive, and newer research links elevated manganese to neurological effects in children. It is one of the most common private well problems in New England.
By county, from homeowner tests
Share of private wells above the state guidance level (300 ug/L) in tests homeowners sent to the state lab, 2006 to 2020.
| County | Wells tested | Above state level | Highest | |
|---|---|---|---|---|
| Strafford | 442 | 8% | 6,400 ug/L | |
| Coos | 429 | 7% | 12,400 ug/L | |
| Sullivan | 608 | 7% | 20,300 ug/L | |
| Merrimack | 4,208 | 7% | 43,300 ug/L | |
| Rockingham | 2,784 | 7% | 24,700 ug/L | |
| Hillsborough | 3,290 | 7% | 4,200 ug/L | |
| Belknap | 1,470 | 6% | 6,000 ug/L | |
| Cheshire | 451 | 5% | 2,400 ug/L | |
| Grafton | 2,113 | 5% | 19,100 ug/L | |
| Carroll | 1,636 | 3% | 10,600 ug/L |
Towns with the highest share above the state level
- Epsom, Merrimack County20% of 133 wells
- Dunbarton, Merrimack County19% of 120 wells
- Fremont, Rockingham County18% of 45 wells
- Bedford, Hillsborough County16% of 609 wells
- Mont Vernon, Hillsborough County15% of 41 wells
- Pittsfield, Merrimack County14% of 56 wells
- Raymond, Rockingham County14% of 50 wells
- Pembroke, Merrimack County14% of 96 wells
- Groton, Grafton County13% of 30 wells
- Sugar Hill, Grafton County13% of 39 wells
- Barnstead, Belknap County12% of 173 wells
- Deerfield, Rockingham County12% of 134 wells
- Strafford, Strafford County11% of 88 wells
- Hampstead, Rockingham County11% of 106 wells
- Sandown, Rockingham County11% of 65 wells
- Canterbury, Merrimack County11% of 160 wells
- Rindge, Cheshire County11% of 114 wells
- Pittsburg, Coos County11% of 57 wells
- Whitefield, Coos County11% of 38 wells
- Warren, Grafton County10% of 39 wells
- Sunapee, Sullivan County10% of 176 wells
- Goffstown, Hillsborough County10% of 119 wells
- Salem, Rockingham County10% of 90 wells
- Claremont, Sullivan County10% of 30 wells
- Atkinson, Rockingham County10% of 102 wells
By county, from individual samples
Public monitoring samples against the EPA limit; counties with at least 30 samples.
| County | Samples | Detected | Above EPA limit | Median | Highest |
|---|---|---|---|---|---|
| Rockingham | 385 | 86% | no limit | 90 | 2,150 ug/L |
| Strafford | 95 | 83% | no limit | 40 | 3,100 ug/L |
| Cheshire | 68 | 81% | no limit | 54.5 | 2,000 ug/L |
| Hillsborough | 432 | 81% | no limit | 0 | 2,880 ug/L |
| Sullivan | 56 | 71% | no limit | 20.1 | 3,460 ug/L |
| Grafton | 244 | 71% | no limit | 30 | 909 ug/L |
| Merrimack | 542 | 70% | no limit | 40 | 3,700 ug/L |
| Carroll | 270 | 69% | no limit | 20 | 2,500 ug/L |
| Belknap | 171 | 64% | no limit | 30 | 1,250 ug/L |
| Coos | 170 | 62% | no limit | 22.5 | 4,400 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. manganese counts and shares are listed on each county and town page with their sources.