Nitrate in New Hampshire well water
In New Hampshire, <1% of 18,081 private wells tested between 2006 and 2020 had nitrate above the New Hampshire guidance level (10 mg/L), according to NH DHHS.
Nitrate reaches wells from fertilizer, septic systems and manure. Above the limit it can cause methemoglobinemia (blue baby syndrome) in infants under six months, and long-term exposure is associated with some cancers. Shallow and dug wells near farmland or dense septic systems are most at risk.
Check your nitrate number
Type the value from your lab report. It is compared to the New Hampshire guidance level and the EPA limit, the same way the full interpretation does it.
Test your New Hampshire well for nitrate
Certified lab analysis of your own tap water, bottles and prepaid return shipping included. The Essential well panel covers arsenic, uranium, nitrate, lead, copper, manganese, iron, sodium and bacteria; radon and PFAS are add-ons.
Order the Tap Score well water test kit, from $209Already tested? Upload the report
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Systems that remove nitrate
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Some links below are affiliate links. If you buy through one, the merchant pays us a commission at no extra cost to you. It does not change which products we list or what the data says.
For nitrate
Under-sink reverse osmosis system
under-sink or countertop, about $300
Look for NSF/ANSI 58 certification listing the contaminant you need removed.
For nitrate
Aquasana SmartFlow reverse osmosis
under-sink or countertop, about $225
Certified to NSF/ANSI 58 and 53 to reduce arsenic (96%, pentavalent), fluoride (90%), lead (99%), nitrate, nitrite and PFOA/PFOS at the kitchen tap, with a remineralizer.
Rather have it installed and sized for your well? Book a free in-home water test with a licensed local company.
Where to get a well tested for nitrate in New Hampshire: certified labs, state programs and prices.
By county, from homeowner tests
Share of private wells above the state guidance level (10 mg/L) in tests homeowners sent to the state lab, 2006 to 2020.
| County | Above state level | Wells tested | Highest |
|---|---|---|---|
| Rockingham | 2,331 | 42 mg/L | |
| Strafford | 542 | 11 mg/L | |
| Hillsborough | 2,119 | 34 mg/L | |
| Merrimack | 4,875 | 21 mg/L | |
| Carroll | 1,819 | 40 mg/L | |
| Cheshire | 637 | 14 mg/L | |
| Grafton | 2,687 | 20 mg/L | |
| Coos | 603 | 18 mg/L | |
| Sullivan | 733 | 10 mg/L | |
| Belknap | 1,735 | 15 mg/L |
Towns with the highest share above the state level
- Newton, Rockingham County8% of 51 wells
- Salem, Rockingham County4% of 72 wells
- Ossipee, Carroll County4% of 144 wells
- Hillsborough, Hillsborough County3% of 222 wells
- Windham, Rockingham County3% of 268 wells
- Stratford, Coos County3% of 34 wells
- Danville, Rockingham County3% of 36 wells
- Kingston, Rockingham County3% of 75 wells
- Fremont, Rockingham County2% of 44 wells
- Durham, Strafford County2% of 43 wells
- Derry, Rockingham County2% of 91 wells
- Francestown, Hillsborough County2% of 45 wells
- Madbury, Strafford County2% of 49 wells
- Stoddard, Cheshire County2% of 54 wells
- Bethlehem, Grafton County2% of 56 wells
- Chester, Rockingham County2% of 58 wells
- Plaistow, Rockingham County2% of 194 wells
- Canterbury, Merrimack County2% of 198 wells
- Webster, Merrimack County1% of 147 wells
- Pittsfield, Merrimack County1% of 71 wells
- Temple, Hillsborough County1% of 69 wells
- Barrington, Strafford County1% of 76 wells
- Amherst, Hillsborough County1% of 75 wells
- Hooksett, Merrimack County1% of 171 wells
- Thornton, Grafton County1% of 160 wells
By county, from individual samples
Public monitoring samples against the EPA limit (10 mg/L); counties with at least 30 samples.
| County | Above EPA limit | Samples | Detected | Median | Highest |
|---|---|---|---|---|---|
| Strafford | 96 | 56% | 0.2 | 19 mg/L | |
| Cheshire | 90 | 57% | 0 | 19.9 mg/L | |
| Sullivan | 62 | 66% | 0.215 | 37.2 mg/L | |
| Carroll | 355 | 61% | 0.1 | 14 mg/L | |
| Merrimack | 564 | 40% | 0 | 24.5 mg/L | |
| Rockingham | 294 | 45% | 0 | 19 mg/L | |
| Coos | 210 | 54% | 0.063 | 11.8 mg/L | |
| Grafton | 283 | 48% | 0 | 11.7 mg/L | |
| Hillsborough | 336 | 69% | 0.1 | 16 mg/L | |
| Belknap | 198 | 32% | 0 | 4.69 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. nitrate counts and shares are listed on each county and town page with their sources.
Analysis: Nitrate in private wells, decade by decade, from the same public records.