Radon in Well Water in Wisconsin

Most radon advice starts with the soil under your foundation. If you live in parts of Wisconsin and draw your water from a private well, there is a second path worth knowing about: radon can dissolve into the groundwater itself, then leave the water and enter the air inside your home every time you shower, run the dishwasher, or wash a load of laundry. Badger State Radon is a free matching service, not a contractor, so this page explains how well-water radon works in plain terms and connects you with independent local radon professionals who handle the testing and treatment.

How radon gets into water and then into the air

Radon is a naturally occurring radioactive gas produced as uranium breaks down in rock and soil. Where groundwater flows through uranium-bearing rock, some of that radon dissolves and travels with the water into a well. It stays in solution under pressure inside the pipes, but the moment the water is agitated or exposed to air (running a faucet, filling the tub, or spraying through a showerhead) the radon comes out of solution and mixes into the room air.

The working rule the Wisconsin DNR uses is that about 10,000 pCi/L of radon in water adds roughly 1 pCi/L to indoor air. The uses that release the most are the ones that aerate warm water, so bathrooms and laundry areas tend to see the biggest jump while the water is running. In practice this means a private well can quietly add to the indoor air level you would read on a radon air test, layered on top of whatever radon is already rising through the foundation. The water is rarely the whole story, but on the wrong well it is a real contributor.

Because the gas escapes into the air during everyday use, the main way waterborne radon reaches you is by breathing it, not by drinking it. That is also why the fix, when one is needed, aims to release or capture the radon before the water is used inside the house rather than only at the kitchen tap. It also explains why a well can matter even if the household drinks bottled or filtered water: the shower, the dishwasher, and the washing machine still release radon into the same air everyone breathes.

Whose water is at risk

This is a private-well issue. Public and municipal water systems in Wisconsin are treated and typically aerated before delivery, which releases dissolved radon well before the water reaches your home, so households on city water rarely need to think about radon in their water at all. A private well draws straight from the aquifer with no such step, and testing is the homeowner's responsibility rather than a utility's.

Within the private-well population, dissolved radon is not spread evenly. The highest levels track the geology: the granite and granitic sand and gravel formations of northcentral and northwestern Wisconsin tend to hold the most radon in groundwater. That puts communities like Wausau in Marathon County and Stevens Point in Portage County among the places where a home on a private well warrants a look at the water, not just the air. Even there, many wells test fine, so the point is not to assume the worst but to actually measure.

Testing your well

If your home is on a private well, testing the water is worth doing, and it is a separate test from an air test. A radon air test measures the gas in the room air and reports in pCi/L of air; a water radon test measures the dissolved radon in a collected water sample, which a lab analyzes and reports in pCi/L of water. One number does not substitute for the other, and a low air test does not prove the water is clear. The scales are different too: water results are reported in the thousands of pCi/L, which is why the DNR treatment threshold sits far above the 4.0 pCi/L figure used for air.

The Wisconsin DNR guidance on testing a private well covers how to collect a sample, how to keep it valid, and where to send it. Because private wells are not monitored the way public systems are, no one tests the water for you. If you are already arranging an air test, ask whether the same provider can collect a water sample on the same visit. For the full walkthrough, see our guide to radon in well water in Wisconsin.

Treatment options

When a water test comes back high, treatment happens at the water, not the air. The Wisconsin DNR suggests considering treatment when well-water radon runs above 4,000 pCi/L. Two methods are common, and both treat the water where it enters the house so the whole home benefits:

• Aeration: the water passes through a tank where air is bubbled through it, releasing the radon so it can be vented outside before the water is used indoors. The DNR describes aeration as the most effective option. A system runs about $3,500.
• Granular activated carbon (GAC): the water passes through a carbon filter that captures radon. GAC is also used, but it usually needs pretreatment to handle iron, sediment, or other water conditions, and the captured radon can accumulate in the filter over time.

Whichever route fits your well, a water radon treatment system is a plumbing installation. It needs plumbing approval from the Wisconsin Department of Safety and Professional Services (DSPS), and the DNR asks that you call the department before installing one so the setup meets code. This is work for a qualified professional rather than a weekend project, which is where a match to a local contractor helps. Treatment is installed where the water enters the home, a point-of-entry setup, so every fixture is covered; treating only the drinking-water tap would leave the shower and laundry releasing radon into the air. Sizing, venting the released gas outdoors, and keeping the system serviceable are all part of a proper install, which is another reason to have the water tested first and let the numbers, not guesswork, decide whether treatment is warranted.

Air first, then water

For most homes the larger exposure by far is the soil gas rising through the foundation, not the water, so the order matters: test the air first. Radon is the leading cause of lung cancer among people who do not smoke and is linked to about 21,000 US lung cancer deaths a year, which is why the air side comes first. If an air test reads at or above the EPA action level of 4.0 pCi/L, address the air with a mitigation system.

Then, if you are on a private well in one of the higher-radon areas, treat the water as the second step, tested and, if needed, treated separately from the air. Start with radon testing to get an air number, and see radon mitigation for how the air side is fixed. When you are ready, we connect you with independent local radon professionals who can look at both the air and the water, so you get one plan instead of two disconnected quotes.