On a Private Well? Radon Can Come Through the Water, Too.

Radon in Well Water in Pennington County

Most radon in homes comes up from the soil — but if your home is on a private well, there's a second pathway worth understanding. Radon dissolves into groundwater as it passes through uranium-bearing rock, and that radon is released into the air of your home whenever you run water — showering, doing laundry, running the dishwasher. Public water systems are treated and aerated so this is rarely an issue, but a private well draws straight from the ground, so waterborne radon can add to the level in the air.

Two different exposures

Radon in water carries two kinds of risk. The larger one is inhalation — radon released from the water into household air adds to what you breathe. A rough rule of thumb used in the field is that roughly 10,000 pCi/L of radon in water can contribute about 1 pCi/L to the air. There's also a smaller ingestion risk from drinking the water directly. Because the air pathway usually dominates, radon-in-water is often investigated when a home already has elevated air radon and is on a well.

Testing the water

Water radon is a separate test from an air test — a water sample is collected carefully (radon escapes if the sample is aerated or left sitting) and analyzed by a lab. If your air radon is high and you're on a well, testing the water tells you whether the well is a meaningful contributor or whether the soil is the whole story. That distinction matters because the fix is completely different.

How waterborne radon is treated

• Aeration — the preferred method for higher levels. Water is agitated with air in a sealed tank so the radon comes out of solution and is vented safely outside before the water reaches your taps. Aeration is highly effective and doesn't concentrate radioactivity the way the alternative can.
• Granular activated carbon (GAC) — for lower levels, water is run through a carbon filter that captures radon. It's simpler and lower-cost, but the carbon accumulates radioactivity over time and eventually needs careful handling and disposal, so it suits lower concentrations.

Both are point-of-entry systems — they treat the water where it comes into the house, so every tap benefits, which is what you want when the concern is radon released into household air.