On a well? Your water can carry radon too
Radon dissolved in well water releases into the air when the water runs — a separate pathway with its own test and its own fix.
The second way radon gets in
Almost all the radon in a house comes up from the soil as gas. But there’s a second, smaller pathway that only applies to homes on private wells: the water itself.
Groundwater sitting in uranium-bearing rock picks up dissolved radon. Every time that water runs (a shower, a dishwasher, a washing machine) some of the gas comes out of the water and into the indoor air. Hot, agitated water releases the most, which is why the shower is the classic example.
Inside Sioux Falls city limits this is mostly a non-issue, since municipal water sheds its radon during treatment and storage. The question belongs to the metro’s well households: acreages outside town, rural homes around the smaller towns, hobby farms on their own wells.
The industry’s rule of thumb puts the pathway in proportion: it takes very roughly 10,000 picocuries per liter of radon in water to add about 1 pCi/L to the air in the house. So water is rarely the main story. But in a home with a strong well source, it can be the reason air numbers stay stubborn. A water test, drawn correctly and lab-analyzed, is how you find out whether the well is contributing. The testing guide covers how the air side gets measured.
Which fix, or both
The two pathways get two different treatments, and the order matters.
Air first. The soil-gas route dwarfs the water route in nearly every home, so the sequence that makes sense is an air test, then soil-gas mitigation if the number is high, then a retest. For most well households, that alone brings the house below the action level, and the water question never needs answering.
Water treatment earns its place when testing shows the well itself carries a heavy load. The usual tool is aeration: a tank that bubbles air through the incoming water so the radon escapes and vents outdoors before the water enters the plumbing. Granular activated carbon shows up on smaller loads, with its own maintenance trade-offs. Which fits, and whether either is worth it, comes down to the water number, the household’s usage, and what the air readings do after soil-gas mitigation.
What this page won’t do is prescribe from a distance. A well home with a high air reading needs its situation assessed as one system (soil, slab, and well) before anyone names a fix. Testing both pathways is cheap information, and it’s the honest place to start.
On a well and wondering? Testing settles it
Frequently Asked Questions
How does radon get into water in the first place?
Groundwater moving through uranium-bearing rock and soil picks up dissolved radon the same way it picks up minerals. When that water comes out of a tap or showerhead, some of the gas escapes into the room air.
Does city water have this problem?
Generally no. Municipal water spends time in treatment and storage, which lets dissolved radon escape before it reaches the tap. This is a private-well question — mostly for acreages and rural homes around the metro, not houses on Sioux Falls city water.
How is water treatment different from a radon system?
An air system pulls soil gas from under the house. Water treatment strips radon from the well supply before it enters the plumbing — typically aeration, sometimes carbon. They solve different pathways, and a well home with high air readings may need the soil-gas fix, the water fix, or both.