Sodium in New Hampshire well water
In New Hampshire, 37% of 17,415 private wells tested between 2006 and 2020 had sodium above the New Hampshire guidance level (20 mg/L), according to NH DHHS.
Sodium enters wells with road salt and from softeners. EPA's guidance level of 20 mg/L matters for people on sodium-restricted diets; most people are not affected below 250 mg/L.
By county, from homeowner tests
Share of private wells above the state guidance level (20 mg/L) in tests homeowners sent to the state lab, 2006 to 2020.
| County | Wells tested | Above state level | Highest | |
|---|---|---|---|---|
| Rockingham | 2,769 | 56% | 747 mg/L | |
| Strafford | 472 | 46% | 687 mg/L | |
| Hillsborough | 3,286 | 43% | 633 mg/L | |
| Belknap | 1,473 | 34% | 1,335 mg/L | |
| Merrimack | 4,194 | 32% | 2,186 mg/L | |
| Carroll | 1,627 | 29% | 699 mg/L | |
| Cheshire | 450 | 28% | 550 mg/L | |
| Grafton | 2,110 | 23% | 1,106 mg/L | |
| Sullivan | 607 | 21% | 478 mg/L | |
| Coos | 427 | 20% | 348 mg/L |
Towns with the highest share above the state level
- Greenland, Rockingham County83% of 36 wells
- Stratham, Rockingham County81% of 101 wells
- Plaistow, Rockingham County81% of 253 wells
- Hampton Falls, Rockingham County76% of 33 wells
- Atkinson, Rockingham County75% of 101 wells
- Kingston, Rockingham County75% of 71 wells
- Brentwood, Rockingham County75% of 47 wells
- Rollinsford, Strafford County73% of 37 wells
- Lee, Strafford County73% of 33 wells
- Durham, Strafford County71% of 52 wells
- Bedford, Hillsborough County71% of 606 wells
- Hooksett, Merrimack County70% of 135 wells
- Hampstead, Rockingham County66% of 106 wells
- Salem, Rockingham County64% of 88 wells
- Dover, Strafford County59% of 32 wells
- Pembroke, Merrimack County57% of 96 wells
- Epping, Rockingham County57% of 30 wells
- Londonderry, Rockingham County56% of 333 wells
- Mont Vernon, Hillsborough County56% of 39 wells
- Windham, Rockingham County53% of 453 wells
- Derry, Rockingham County53% of 102 wells
- Newton, Rockingham County50% of 42 wells
- South Hampton, Rockingham County50% of 36 wells
- Pelham, Hillsborough County49% of 124 wells
- Bow, Merrimack County49% of 553 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 | 328 | 99% | no limit | 16 | 258 mg/L |
| Cheshire | 67 | 97% | no limit | 8 | 76 mg/L |
| Carroll | 247 | 96% | no limit | 9 | 390 mg/L |
| Hillsborough | 260 | 96% | no limit | 12.3 | 540 mg/L |
| Strafford | 91 | 96% | no limit | 11 | 510 mg/L |
| Sullivan | 39 | 95% | no limit | 6.9 | 160 mg/L |
| Merrimack | 460 | 92% | no limit | 9 | 184 mg/L |
| Coos | 159 | 89% | no limit | 5.8 | 300 mg/L |
| Grafton | 214 | 88% | no limit | 7 | 570 mg/L |
| Belknap | 160 | 87% | no limit | 9 | 225 mg/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. sodium counts and shares are listed on each county and town page with their sources.