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Well water testing in Rockingham County, New Hampshire
How common arsenic and radon are in Rockingham County wells, what New Hampshire recommends you test for and how often, which towns require testing, and where to get a sample analyzed, with a source for every fact.
How many people here use a private well
USGS estimates that about 142,000 people in Rockingham County supplied their own household water in 2015, about 47% of the county's population.1 Statewide, NHDES says nearly half of New Hampshire residents get their water from a private well.2
What tests in Rockingham County have found
Arsenic
- State lab results (2006–August 2020): in private well samples tested at the NH Public Health Laboratories, 31% of Rockingham County wells were over 0.005 mg/L (5 µg/L) arsenic, compared with 25% statewide.3
- A random USGS sample: in a USGS study of randomly selected private bedrock wells in southeastern New Hampshire, 26% of 125 Rockingham County samples had more than 5 µg/L of arsenic, 14% had more than 10 µg/L, and 2% had more than 50 µg/L. The highest result in the study, 0.215 mg/L, was in Rockingham County.4
- A national model: a USGS model estimates that about 21,400 domestic-well users in Rockingham County (95% confidence range about 16,700–27,000, based on 2010 population) have well water with predicted arsenic above 10 µg/L.5 That's a model estimate and can't predict any single well.
NHDES estimates that 25–30% of private residential wells statewide have arsenic at 5 ppb or higher. New Hampshire's 5 ppb arsenic standard (in effect since July 1, 2021) applies to public water systems, not private wells.6
Radon, uranium and other results
From the same 2006–2020 state lab data for Rockingham County:3
| Test | Level used | Rockingham County | Statewide |
|---|---|---|---|
| Radon (testing advisory) | over 2,000 pCi/L | 32% | 30% |
| Sodium | over 20 mg/L | 55% | 34% |
| Iron | over 0.3 mg/L | 14% | 17% |
| Lead (stagnant sample) | over 0.015 mg/L | 12% | 13% |
| Copper (stagnant sample) | over 1.3 mg/L | 10% | 12% |
| Chloride | over 250 mg/L | 7% | 3% |
| Manganese | over 0.30 mg/L | 6% | 5% |
| Uranium | over 30 µg/L | 4% | 4% |
| Nitrate | over 10 mg/L | 1% | 0% |
The source table lists the uranium limit as "30 mg/L". We read that as 30 µg/L, which is the EPA uranium standard.8
These are wells whose owners chose to test at the state lab, not a random sample. NHDES notes the data don't include private labs.3 For town-level numbers, see the NH DHHS Private Well Water Quality Dashboard.
PFAS
NHDES has been sampling private wells for PFAS since 2016. On the NH PFAS Response website, a "Sampling Dashboard" shows existing results, and a "Private Well Testing Request Form" lets you ask NHDES to sample your well.7
Does New Hampshire require testing?
NHDES says there is no statewide testing or treatment requirement for private wells, but some towns require it.3 As of NHDES's September 2021 presentation, Derry, Salem, Windham and Chester (all in Rockingham County) were among the towns requiring well water testing to get a certificate of occupancy, generally using NHDES's Standard Analysis list.3 Check with your town for its current rules.
What to test for and how often
NHDES's April 2026 guidance recommends testing for:7
- Arsenic, bacteria (total coliform and E. coli), chloride, copper and lead (stagnant and flushed samples), fluoride, hardness, iron, manganese, nitrate, nitrite, pH, radon, sodium and uranium
- PFAS: PFHxS, PFNA, PFOA and PFOS
When to test:7
| Who | When |
|---|---|
| Private well users | Bacteria, nitrate and nitrite every year. Everything else on the list every 3–5 years. |
| Home buyers | Before buying a home with a private well, if the seller hasn't provided a recent test. |
| After installing treatment | Test the treated water to confirm it's working, then every 3–5 years. |
NHDES notes that PFAS sampling can be costly. If a first PFAS test finds none and your budget doesn't allow retesting every 3–5 years, NHDES says it's acceptable to wait longer, especially if nearby land uses don't change.7
Where to get tested and treatment options
Who to contact
| Contact | Details |
|---|---|
| NHDES private well testing | WellTest@des.nh.gov3 |
| NHDES (main office) | 29 Hazen Drive, Concord, NH 03302-0095 · (603) 271-35032 |
| Lab accreditation questions (NHELAP) | (603) 271-2998 / (603) 271-5314 · nhelap@des.nh.gov7 |
Related guides
- How to read your well water test results
- How often to test a private well
- Best way to test well water
- All New Hampshire county pages
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Dieter, C.A., and others, 2018, Estimated Use of Water in the United States County-Level Data for 2015 (ver. 2.0), U.S. Geological Survey data release (domestic self-supplied population). https://doi.org/10.5066/F7TB15V5 ↩
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NHDES, "Private Wells." https://www.des.nh.gov/water/drinking-water/private-wells ↩↩↩
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Kernen, B., NHDES, "Private Wells in Portsmouth" (presentation, September 1, 2021; data: EPHT combined NHDES/NH Public Health Laboratories data set, 2006–August 2020), hosted by the City of Portsmouth. https://www.portsmouthnh.gov/sites/default/files/2021-09/Portsmouth%20SWAG%20Sep%201%202021%20DES.pdf ↩↩↩↩↩↩
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U.S. Geological Survey, "Arsenic Concentrations in Private Bedrock Wells in Southeastern New Hampshire," Fact Sheet 051-03 (2003), table 1. https://pubs.usgs.gov/fs/fs-051-03/ ↩
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Ayotte, J.D., Medalie, L., and Qi, S.L., 2017, Estimated county level domestic well population with arsenic greater than 10 micrograms per liter based on probability estimates for the conterminous U.S., U.S. Geological Survey data release. https://doi.org/10.5066/F7CN724V ↩
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NHDES, "More Protective Arsenic Standard Will Reduce Risk for Many" (March 8, 2021). https://www.des.nh.gov/news-and-media/blog/more-protective-arsenic-standard-will-reduce-risk-many ↩
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NHDES, "Water Testing Guidance for Private Well Users" (April 2026; lab list updated 9/20/2024). https://www.des.nh.gov/sites/g/files/ehbemt341/files/documents/labs-private-wells.pdf ↩↩↩↩↩↩↩
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U.S. EPA, "Radionuclides Rule." https://www.epa.gov/dwreginfo/radionuclides-rule ↩