Radon
Rn·Affects lungs
A radioactive noble gas produced by uranium decay. The second-leading cause of lung cancer in the US, with shower-water aerosolization a documented exposure route.
Rn
EPA limit
No enforceable MCL (proposed 300 pCi/L)
Most at risk
Well-water households in granite belts (New England, Appalachia, Rocky Mountains, parts of the Upper Midwest)
Found in
Well water
AquaOx filters
YesActivated coconut shell carbon (waterborne radon)
What it does to you
Health effects
Radon is classified by the EPA as the second-leading cause of lung cancer in the United States, behind tobacco. As a noble gas it does not bind chemically in the body, but its decay products (radon daughters: polonium-218, lead-214, bismuth-214, polonium-214) are charged particles that lodge in lung tissue and deliver concentrated alpha-radiation doses to nearby cells.
Most radon exposure comes from inhaled air, primarily from soil-gas seepage into basements and ground-level living spaces. Waterborne radon contributes a smaller but real fraction: hot showers, dishwashers, and washing machines aerosolize dissolved radon out of the water and into household air, where it is then inhaled.
Direct ingestion of radon in drinking water also carries a smaller, measurable risk of stomach and gastrointestinal cancer, though the lung-cancer pathway through inhaled aerosolized radon dominates the total exposure budget for households with high waterborne concentrations.
Where it comes from
How it gets into your water
Radon forms continuously as uranium decays in soil and bedrock. Because it is a gas, it migrates upward through fractures, accumulating in basements and dissolving into groundwater as it moves. Wells drilled into granite, gneiss, and certain shale formations frequently contain elevated radon.
US hotspots for waterborne radon include New England (especially New Hampshire, Maine, and Massachusetts), the Appalachian granite belt, the Rocky Mountains, and parts of the Upper Midwest. Surface water supplies typically have very low radon because the gas vents to the atmosphere before reaching the tap; the issue is almost exclusively a well-water concern.
Municipal systems that use groundwater also occasionally exceed elevated levels, but aeration during storage and treatment usually reduces concentrations substantially before delivery.
Granite bedrock wells
Most common source of waterborne radon
Soil gas migration
Drives both air and waterborne radon
Hot showers and laundry
Aerosolize dissolved radon into household air
Uranium decay in aquifers
Continuous production wherever uranium is present
Find out for yourself
Is it in your water?
Radon in drinking water is not currently regulated under an enforceable EPA standard. The EPA proposed an MCL of 300 pCi/L (with an Alternative MCL of 4,000 pCi/L for systems that also address indoor air radon), but the rule has been stalled since 1999. Most public utilities do not routinely report radon in their Consumer Confidence Reports.
Private well owners in known granite-belt regions should test independently. State radon programs offer subsidized water testing in most affected states, and certified labs run a standard radon-in-water panel for around $30 to $50. The EPA also recommends testing indoor air for radon (action level 4 pCi/L in air) since the air-side risk is typically larger than the water-side risk.
The fix
How AquaOx filters it
Activated carbon is effective at capturing waterborne radon. The coconut shell carbon stage in the AquaOx whole-house system adsorbs dissolved radon as water passes through, reducing the concentration that reaches showers and household appliances where it would otherwise aerosolize.
For households with very high waterborne radon (above roughly 5,000 pCi/L), a dedicated aeration system is generally preferred over carbon, because trapped radon decay products will accumulate in the carbon bed over time and require careful handling. At more typical concentrations, the AquaOx coconut shell carbon stage handles the load well.
Critically, water treatment only addresses the waterborne fraction. If your home tests above 4 pCi/L for radon in indoor air, you also need a soil-side mitigation system (a sub-slab depressurization fan), which is separate from any water filtration. Always test both water and air before selecting equipment.