Radon in well water in NH: testing, aeration and carbon filters

If your home is on a drilled (bedrock) well in Nashua’s surrounding towns, radon can reach you two ways: up from the ground and out of the tap. This guide goes beyond the basic thresholds: how water radon turns into air radon, how to read results in the gray zone, how to sample, how aeration and carbon filters compare, and what else to test a bedrock well for.

How radon gets from a bedrock well into your air

NHDES says radon is commonly found in New Hampshire bedrock and in water from bedrock (drilled) wells. Dug wells and point wells tend to have little to no radon (NHDES). Radon is highly soluble in water, and a bedrock well can have high levels even when nearby bedrock wells are low (NHDES). Testing your own well is the only way to know.

Once the water is inside, radon escapes into the air when you shower, wash dishes or do laundry (NHDES). NH DHHS adds faucets and toilets to that list (NH DHHS). The EPA explains that most of the risk from radon in water comes from breathing radon released this way. Drinking it carries a much smaller risk. The EPA also says radon entering through the soil is usually a much larger risk than radon entering through water (EPA). That’s why both NHDES and the EPA say to test the air too, not just the water.

Reading your numbers: NHDES guidance and the 2,000–10,000 pCi/L gray zone

There are no federal or state standards for radon in drinking water, only advisories (NHDES). NHDES recommends:

Source: NHDES fact sheet DWGB-3-12. NH DHHS words the middle band as considering water treatment when the air level is 4 pCi/L or more (NH DHHS).

Why the middle band depends on your air result. The rule of thumb from NHDES and NH DHHS is that every 10,000 pCi/L of radon in water adds about 1 pCi/L to indoor air (NHDES, NH DHHS). By that rule, water in the 2,000–10,000 range adds only about 0.2 to 1 pCi/L to your air. That’s an estimate, not a measurement. So:

• Water in the gray zone, air below 4 pCi/L: NHDES’s guidance doesn’t call for water treatment. Keep retesting. Remember that the EPA still suggests considering an air fix between 2 and 4 pCi/L (EPA).
• Water in the gray zone, air above 4 pCi/L: water treatment may be advisable. By the rule of thumb, the water explains only part of that number, so ask a pro how much of your result the water explains and whether an air system alone would get you where you want to be.
• Water at 10,000 pCi/L or more: NHDES recommends treating the water and mitigating the air.

For context, NHDES says long-term radon exposure is estimated to cause about 100 deaths of New Hampshire residents a year, and that any amount of radon in air or water increases lung cancer risk (NHDES).

How to sample your well water

1. Use an accredited lab. NHDES publishes a list of labs accredited by the New Hampshire Environmental Laboratory Accreditation Program that serve private well users. It also points to its online Accredited Laboratory Search for current listings (NHDES). Get your sample bottles and instructions from the lab (NHDES).
2. Test at least twice. Radon in well water can vary a lot from one test to the next. NHDES recommends at least two radon tests, at least a month apart when possible, before you decide on treatment (NHDES).
3. Follow the lab’s collection instructions exactly. Radon is a gas, and the water-testing procedure is different from an air test (EPA).
4. Add the other radiological tests at the same time (see below). NHDES notes some labs offer radon, uranium and gross alpha as a package (NHDES).
5. Test the air as well. NH residents can order a free short-term air kit (NHDES). See our radon testing guide.

NHDES also offers a free online tool, Be Well Informed, where you can enter your water results to see health information and treatment options (NHDES).

Aeration vs. granular activated carbon (GAC)

Radon has to be treated for the whole house (point-of-entry), because it is released from every tap and shower. A kitchen-sink filter won’t stop it (NHDES, EPA). The two whole-house options are:

About cost: we haven’t found a current, official New Hampshire price range for radon water treatment, so we don’t quote one. Get a written quote that lists the equipment, venting, any maintenance contract and a post-installation water test. Weigh the upkeep too, not just the purchase price.

After a treatment system goes in, NHDES recommends testing the treated water to confirm it works, then servicing the system and retesting the treated water every 3–5 years (NHDES).

Testing a bedrock well for uranium and gross alpha

NHDES says radon isn’t the only naturally radioactive substance in New Hampshire well water. A well that is high in radon is more likely to be high in uranium and/or gross alpha (NHDES). NHDES cites a USGS study of bedrock wells in the northeastern U.S. that found about 15% exceeded the health standard for uranium and about 12% for alpha particle radiation (NHDES).

Source: NHDES fact sheet DWGB-3-11.

NHDES suggests this order:

1. Collect samples for radon, uranium, gross alpha and radium-226/228. Ask the lab to hold the radium samples.
2. If gross alpha is above 5 pCi/L, have the lab run radium-226/228. Combined radium above 5 pCi/L means the well has elevated radium.
3. If analytical gross alpha is above 15 pCi/L, subtract the uranium activity. If the net result is still above 15 pCi/L, treatment is required. (NHDES)

The fixes are different from radon. Uranium, radium and gross alpha aren’t volatile, so NHDES says they can be treated at the kitchen sink (point-of-use). Options include reverse osmosis, which wastes 3–5 gallons of water for every gallon treated, or anion exchange for uranium. Whole-house ion exchange is another option. NHDES warns that anion resin must be followed by a calcite neutralizer, or lead and copper can leach from your plumbing. It also says resin brine should go to the septic system, not a drywell (NHDES).

Who installs radon water treatment in New Hampshire?

• Radon in air: since January 1, 2015, radon-in-air mitigation designers and installers must be nationally certified (NHDES). Check names on the NRPP site.
• Radon in water: NH has no certification requirement for radon-in-water treatment (NHDES). NH DHHS notes that installers may need a plumbing license (NH DHHS).
• Water treatment technicians: New Hampshire’s Mechanical Licensing Board offers a voluntary water treatment technician certification (NH Saf-Mec rules). It’s fair to ask whether an installer holds it, or a NH plumbing license.

At 10,000 pCi/L or more, NHDES suggests consulting both radon mitigation and water treatment providers (NHDES). Air and water systems are separate installations, so you may be talking with two different specialists. See how air mitigation works.

Homeowner checklist

1. Find out what kind of well you have (drilled/bedrock vs. dug or point).
2. Test your indoor air in the lowest lived-in level.
3. Test the well water for radon through an NHDES-accredited lab, then repeat about a month later.
4. Add uranium and gross alpha (and hold radium samples) to the same lab order.
5. Compare your water and air results with the NHDES table above.
6. If treatment makes sense, get written quotes. Ask about aeration vs. GAC, venting, maintenance, filter disposal and licensing.
7. After installation, retest the treated water and your indoor air. Then retest every 3–5 years.

Quick answers

Nearby and related

Town-specific notes: Milford private wells · Amherst bedrock wells. More answers in the radon FAQ.

If your well has a pump or pressure problem, NH Well Pump Help connects homeowners west of Nashua with local well pump pros. It’s our sister referral site.

Want a local radon pro to look at your air and water results? Request a free quote and choose “Radon in well water.”