Radon in Well Water: Testing, Health Risks, and Treatment...

Most discussions of residential radon focus on soil and rock as the source—radon gas seeping up through foundation cracks and accumulating in basements. But homeowners with private wells have an additional exposure pathway: radon dissolved in groundwater that enters the home through faucets, showers, and appliances.

How Radon Gets Into Well Water

Radon occurs naturally in groundwater in areas with uranium-bearing rock and soil. Private wells drilled into granite, shale, or other radon-bearing formations can draw up water with elevated dissolved radon.

When this water enters your home and is used—particularly in showers, washing machines, or dishwashers—radon off-gasses from the water into indoor air. The shower is the primary exposure point: hot water, agitation, and an enclosed space create ideal conditions for radon to volatilize.

Note: Public water systems treat water before distribution, which significantly reduces waterborne radon levels. This guide primarily applies to private well owners.

Health Risk: Is Waterborne Radon Dangerous?

Waterborne radon contributes to two types of exposure:

Inhalation risk: Radon released from water during showering and household use adds to indoor air radon concentrations. Studies suggest that for every 10,000 pCi/L of radon in water, indoor air radon levels increase by approximately 1 pCi/L.

Ingestion risk: Drinking water containing radon also poses a direct risk, though the lung cancer risk from inhaled radon is far greater. The EPA estimates 89% of waterborne radon risk comes from inhalation, not ingestion.

The EPA has proposed a guidance level of 300 pCi/L for radon in drinking water (from public systems), but for private wells, the risk depends on actual water radon levels combined with how heavily water is used.

How to Test Your Well Water for Radon

Water radon testing requires a specific test—standard air radon kits don’t test water. Options:

Certified laboratory testing: Collect a water sample following the lab’s instructions (usually a special vial, collected from the cold-water tap after running the water for several minutes) and mail it to a certified lab. Cost: $25–$75.

State programs: Many state health departments offer subsidized testing for private well owners, particularly in high-radon geologic areas. Check your state’s department of environmental quality or health.

Combined air and water testing: Some radon mitigation contractors test both air and water as part of an initial assessment.

When to Test

Consider testing well water for radon if:

• Your home has a private well in a state or county with known radon geology (Iowa, Maine, New Hampshire, New England in general, Rocky Mountain states, parts of Appalachia)
• Your indoor air radon tests show levels above 4 pCi/L and you’ve already installed air mitigation
• Your home is in a granite bedrock area—granite is the most common radon-bearing rock for well water

Treatment Options

If your well water tests high for radon, two primary treatment methods exist:

Aeration Treatment (Point-of-Entry)

A point-of-entry aeration system is installed where the well water enters the home. The system agitates the water, releasing dissolved radon into air that is vented outdoors before the water is distributed through the house.

Effectiveness: Removes 95–99% of dissolved radon. Cost: $2,000–$5,000 installed. Maintenance: Requires periodic servicing; the vent must discharge properly to avoid outdoor radon accumulation near the home.

Granular Activated Carbon (GAC) Treatment

A GAC filter installed at the point of entry removes radon from water by adsorption onto the carbon media.

Effectiveness: Very high initially, but the carbon media accumulates radon over time and becomes mildly radioactive. Old GAC filters must be disposed of as low-level radioactive waste, which requires professional handling. Cost: $1,000–$3,500 installed. Limitation: GAC filters are more suitable for lower-radon-level water (under 5,000 pCi/L) due to the disposal complication at high concentrations.

Aeration is generally preferred for higher radon levels and situations where long-term maintenance simplicity is important.

Point-of-Use Filters

Filters at individual faucets (under-sink RO systems, for example) address ingestion risk from drinking water but don’t address the inhalation risk from showering and other hot-water uses. Not a complete solution for waterborne radon.

Do You Need Both Air and Water Mitigation?

If your home has elevated radon in both air and water, you may need to address both. Air mitigation (sub-slab depressurization) addresses soil-sourced radon entering through the foundation; water treatment addresses the additional contribution from the well.

In many cases, water treatment alone can reduce indoor air radon by 1–3 pCi/L when waterborne radon is a major contributor to indoor air levels. An experienced radon professional can assess whether air, water, or both need treatment.

Frequently Asked Questions

Does radon in well water smell or taste different? No. Like air radon, waterborne radon is odorless, colorless, and tasteless. Testing is the only way to know.

Is radon in well water common? It depends heavily on location. In granite bedrock states like New Hampshire and Maine, elevated well water radon is fairly common. In areas with sandstone or sedimentary geology, it’s rare.

If I install an air mitigation system, does that fix the water problem too? No. Sub-slab depressurization treats radon entering from the soil through the foundation. It doesn’t affect radon dissolved in your well water.

How often should I retest well water radon? If your test shows low levels and nothing changes (no new well drilling, no geological events), testing every 5 years is reasonable. If levels were elevated and you installed treatment, retest after treatment and annually thereafter.

Can radon damage my well equipment? Radon itself doesn’t damage pipes or appliances. However, radium (which decays to produce radon) can deposit in water softeners and sediment filters over time, creating a mild radioactivity concern at those components.

For cost information, see our radon mitigation cost guide.

Find Local Radon Testing and Mitigation Specialists

A radon professional certified in both air and water testing can evaluate your complete exposure picture and recommend the appropriate treatment. Use RadonLocal to find certified contractors near you.

For more information, see our radon mitigation cost guide, radon testing guide, and how to choose a radon contractor.