Lead in well water
The county where Lead is found above the limit most often is Coos County, New Hampshire: 17% of 346 private wells tested, according to NH DHHS.
Lead in well water almost always comes from household plumbing and older fixtures, not the aquifer, and corrosive (low pH) well water makes it worse. There is no safe level for children; it harms brain development.
- EPA limit
- 15 ug/L (EPA action level (40 CFR 141.80); 2024 rule lowers to 10 ug/L in 2027)
- New Hampshire level
- 15 ug/L
- CAS number
- 7439-92-1
Where lead is worst, by homeowner tests
Counties ranked by the share of private wells above the state guidance level in tests homeowners sent to the state lab. Shares combine town summaries, weighted by wells tested.
| County | Wells tested | Above state level | Highest | |
|---|---|---|---|---|
| Coos County, New Hampshire | 346 | 17% | 721 ug/L | |
| Cheshire County, New Hampshire | 375 | 17% | 205 ug/L | |
| Sullivan County, New Hampshire | 543 | 15% | 892 ug/L | |
| Hillsborough County, New Hampshire | 1,580 | 15% | 31,200 ug/L | |
| Carroll County, New Hampshire | 1,491 | 14% | 3,820 ug/L | |
| Rockingham County, New Hampshire | 1,737 | 13% | 15,100 ug/L | |
| Merrimack County, New Hampshire | 3,868 | 13% | 2,490 ug/L | |
| Grafton County, New Hampshire | 1,948 | 13% | 10,400 ug/L | |
| Belknap County, New Hampshire | 1,398 | 12% | 1,340 ug/L | |
| Strafford County, New Hampshire | 263 | 9% | 169 ug/L |
By individual samples
Counties with at least 30 individual samples in public monitoring data, against the EPA limit.
| County | Samples | Detected | Above EPA limit | Median |
|---|---|---|---|---|
| Sullivan County, New Hampshire | 32 | 50% | 6% | 0 ug/L |
| Strafford County, New Hampshire | 56 | 48% | 4% | 0 ug/L |
| Merrimack County, New Hampshire | 146 | 58% | 2% | 0.09 ug/L |
| Grafton County, New Hampshire | 73 | 36% | 1% | 0 ug/L |
| Hillsborough County, New Hampshire | 208 | 61% | 0% | 0 ug/L |
| Rockingham County, New Hampshire | 183 | 50% | 0% | 0 ug/L |
| Carroll County, New Hampshire | 69 | 36% | 0% | 0 ug/L |
| Coos County, New Hampshire | 37 | 16% | 0% | 0 ug/L |
How to test
Use a state-certified lab and a proper sampling bottle; hardware-store strips cannot measure lead at the levels that matter. Collect from the kitchen tap before any treatment, and again after treatment if you install it.
How to treat
- Point-of-use reverse osmosis
- Certified lead-removal carbon filter
- Neutralizing filter to raise pH and stop leaching