Radon in well water

Radon can dissolve in groundwater, especially where wells draw from granite and other uranium-bearing rock. Homes on private wells can get some of their indoor radon through the tap.

How water adds radon to indoor air

When water comes out of a faucet or showerhead, or runs through a dishwasher or washing machine, some of the dissolved radon escapes into the air. EPA lists the water supply as one of the ways radon enters homes. For most households the main risk from radon in water is breathing it after it is released, with a smaller risk from drinking it. In most homes, radon from soil gas contributes far more to indoor levels than radon from water, but in areas with very high radon in groundwater the water can matter.

Public water vs private wells

Radon escapes from water that is stored and treated, so homes on large public systems that use surface water (rivers and reservoirs) rarely get much radon from their water. Private wells deliver groundwater directly from the rock to the house. The USGS notes that private well owners are responsible for testing their own water, since federal drinking water rules do not cover private wells.

Is there a federal limit?

No enforceable federal limit for radon in drinking water has been finalized. EPA proposed a radon rule in 1999 that paired a standard for water with programs to reduce radon in indoor air, but it has not been finalized. Some states publish their own guideline levels for radon in well water. Your state radon or drinking water program can tell you what applies.

How to test well water

• Test your indoor air first. If air results are elevated and you have a private well, consider testing the water too.
• Water tests require a special sampling procedure because radon escapes quickly. Get a kit from a certified lab or your state program and follow its instructions exactly, often filling a vial underwater from a tap with no aerator.
• Results are reported in pCi/L of water, which is not the same scale as pCi/L of air.

Treatment options

Two approaches are common for whole-house treatment:

• Aeration systems bubble air through the water and vent the radon outdoors. They are usually the choice for higher levels.
• Granular activated carbon (GAC) filters adsorb radon. They can work for lower levels, but the carbon can accumulate radioactivity, so sizing and disposal need care.

Point-of-use filters at a single tap do not address radon released by showers and appliances. A water treatment professional can recommend a system based on your results.

Related

If you have a well, you may also want our sister topic of general well water testing, including bacteria, nitrate, and arsenic. For radon in air, start with how to test your home.

Testing the rest of your well water

A radon test is not a full water test. For bacteria, nitrate, and the other basics, see well water testing on our sister site Septic & Well Guide.