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Radon and Private Well Water in New Hampshire

Updated 2026-10-10 · 5 min read

Arsenic and radon occur naturally in NH. How often NHDES says to test your well, the radon action level, and who can install treatment or mitigation.

Why this matters in NH

According to NHDES, nearly half of New Hampshire residents get their water from a private well. Arsenic and radon occur naturally in the state's rock and soil, along with manganese and bacteria, and pollutants such as PFAS and MTBE are also found in groundwater.

State drinking water standards apply to public water systems, not private wells, so testing and treating a private well is up to the owner. NHDES recommends that private well users test regularly and install treatment if needed.

How often to test your well

NHDES's water testing guidance for private well users (April 2026) recommends testing for arsenic, bacteria (total coliform and E. coli), chloride, copper, fluoride, hardness, iron, lead, manganese, nitrate, nitrite, pH, radon, sodium, uranium, and four PFAS compounds (PFHxS, PFNA, PFOA and PFOS). On timing, it recommends:

Every year: bacteria, nitrate and nitrite
Every 3 to 5 years: the rest of the list. NHDES notes PFAS testing can be costly, and if a first PFAS test finds none, waiting longer may be reasonable when nearby land uses haven't changed.
Before you buy a home with a private well, if the seller hasn't provided a recent test
After a treatment system is installed: test the treated water to confirm it works, then keep the system maintained and retest treated water every 3 to 5 years

Where to get water tested

NHDES recommends using a lab accredited by the New Hampshire Environmental Laboratory Accreditation Program, and its testing guidance lists accredited labs that serve private well owners. One option is the state's own NH Public Health Laboratories Water Analysis Laboratory in Concord, which tests private well water for a fee and sends homeowners a report with an interpretation of the results.

NHDES has also sampled some private wells for PFAS since 2016, focusing on wells most likely to be affected. You can check its sampling dashboard or submit a request through the NHDES PFAS private wells page, though NHDES says it can't sample every well. That page also links to a PFAS treatment rebate program for private well owners; check there for current eligibility.

Understanding your results

NHDES's free online Be Well Informed tool lets you enter your lab results and see whether anything is above health limits and what kinds of treatment might fit.

Arsenic is a common concern. NHDES estimates that a private well in New Hampshire has about a 25% chance of containing naturally occurring arsenic above 5 parts per billion (ppb), and that wells a short distance apart can have very different water (NHDES fact sheet DWGB-3-2). Since July 1, 2021, New Hampshire's arsenic limit for public water systems has been 5 ppb, half the federal limit of 10 ppb (NHDES). That limit doesn't apply to private wells, but it's a useful benchmark when you read your results.

For PFAS, NHDES recommends at a minimum testing for the four compounds that have state drinking water limits (MCLs) for public water systems: PFOA, PFOS, PFHxS and PFNA (NHDES PFAS).

Radon in the air

Radon is a radioactive gas from the ground that can build up indoors. A 2019 NHDES fact sheet estimates that long-term radon exposure leads to about 100 deaths a year among NH residents (NHDES fact sheet DWGB-3-12). NH DHHS says testing is the only way to know if radon is in your home.

Testing: as of October 2026, the NH DHHS Radon Program offers a free radon test kit to NH residents, which you can request through its testing page, and some public libraries lend radon monitors through a DHHS project. Testers don't have to be certified in NH, though DHHS recommends a nationally certified measurement professional, especially for real estate transactions. Radon tends to be higher in colder months, so DHHS suggests retesting in winter if you tested in warm weather (NH DHHS radon testing).

Fixing it: EPA recommends taking action when indoor air radon is 4 picocuries per liter (pCi/L) or higher. In New Hampshire, contractors who install systems to reduce radon in air must be nationally certified; DHHS points to the NRPP and NRSB lists to find one (NH DHHS radon mitigation). Ask any mitigator for proof of their national certification.

Radon in water

Radon can also be dissolved in well water, mostly in drilled bedrock wells, and released into the air when you shower, do laundry or run water. NH DHHS estimates that every 10,000 pCi/L of radon in water adds roughly 1 pCi/L to indoor air. There's no federal or state standard for radon in drinking water, but NH has advisory guidance (NHDES fact sheet DWGB-3-12; NH DHHS):

At or above 10,000 pCi/L in water, NHDES recommends treating the water along with mitigating radon in the air.
Between 2,000 and 10,000 pCi/L, treating the water may be advisable if radon in the home's air is 4 pCi/L or higher.
NHDES recommends at least two radon-in-water tests, ideally a month or more apart, before deciding on treatment. It also recommends testing bedrock wells for uranium and gross alpha, since wells high in radon are more likely to have those too.
Treatment is usually an aeration system where the water line enters the house. DHHS says charcoal filters aren't very effective above 2,000 pCi/L and can build up radiation.
According to NH DHHS, installers of radon-in-water treatment don't need radon certification, but the installation may require a licensed plumber. See plumbers in our directory.

Drilling a well or replacing a pump

Water well contractors and pump installers must be licensed by the NH Water Well Board. Licensed plumbers and electricians can repair and service well pumps, but NHDES says they need a pump installer license to install or replace one. NHDES has a licensed contractor search. For other trade licensing, see our licensing guide, and for more on testing and new wells, see our well water testing and drilling guide.

If you have a well and a septic system, keep them apart and maintained. Our septic guide covers the state rules.

This guide is general information, not medical advice, and guidance can change. Confirm current recommendations with NHDES or the NH DHHS radon program, and for health questions about test results, contact NH DHHS or your doctor.