Radon in New Hampshire Well Water

NH's granitic geology produces some of the highest radon levels in the country — both in indoor air and in well water. Radon in water is an often-overlooked cancer risk.

How Radon Gets Into Well Water

Radon is a radioactive gas produced by the natural decay of uranium in rock and soil. New Hampshire's granitic bedrock contains trace amounts of uranium throughout, and as this uranium decays, radon gas is released.

Underground, radon dissolves into groundwater. When that water is pumped into your home and used for showering, washing dishes, or running laundry, the radon off-gases into your indoor air. This is in addition to radon that seeps through your foundation from soil — they're the same gas, two different pathways.

Health Risk

Radon is the second leading cause of lung cancer in the United States, after smoking. The EPA estimates radon causes approximately 21,000 lung cancer deaths per year.

The contribution from water-borne radon is smaller than from soil gas, but it's not negligible — EPA estimates that radon in water causes roughly 168 cancer deaths per year nationally. In a high-radon state like NH, the risk is proportionally higher.

Testing

There is no federal standard for radon in drinking water (EPA proposed 300 pCi/L for systems without a mitigation program, and 4,000 pCi/L with one, but these were never finalized).

NH DES recommends testing well water for radon, particularly if:

• Your home has elevated indoor air radon (very common in NH)
• Your well is drilled into bedrock (as opposed to a shallow dug well)
• You're in a known high-radon area (most of NH qualifies)

Radon water testing costs approximately $25-$50 at most certified labs. See our testing guide.

Treatment

Treatment	Typical Cost	Notes
Aeration system	$3,000-$5,000	Most effective. Strips radon from water and vents it outdoors. 95-99% removal.
Granular activated carbon (GAC)	$1,000-$2,500	Adsorbs radon onto carbon. Less effective at very high levels. Spent carbon becomes mildly radioactive — disposal considerations.

Aeration is generally preferred for high radon levels. GAC works well for moderate levels but the carbon needs replacement, and the used carbon contains accumulated radioactive material.