What is Radon?
Radon is a naturally occurring radioactive gas that forms when uranium, thorium, or radium breaks down in soil, rock, and water. It is colorless, tasteless, and odorless, making it virtually undetectable without specialized testing. Although radon is present in the outdoor air at low levels, it becomes a health concern when it accumulates indoors—especially in confined areas such as basements or well water systems.
As radon decays, it releases radioactive particles that can be inhaled or ingested. Over time, exposure to high levels of radon can damage lung tissue and increase the risk of lung cancer. According to the U.S. Environmental Protection Agency (EPA), radon is the second leading cause of lung cancer in the United States, behind only smoking.
How Does Radon Get Into Groundwater?
Radon enters groundwater through the natural movement of water through soil and rock that contains uranium and radium. As these radioactive elements decay, radon gas is released and dissolves into the surrounding groundwater. Private wells that draw water from bedrock aquifers, particularly granite or shale formations, are more likely to contain higher levels of radon.
Unlike surface water (from lakes or rivers), which tends to lose radon quickly due to exposure to air and sunlight, groundwater remains in contact with bedrock for long periods, giving radon more time to dissolve. If this water is pumped into a home and used for drinking, cooking, or bathing, radon can be released into the indoor air or ingested directly.
The transfer of radon from water to air is particularly significant during activities like showering or running the dishwasher, where water is agitated or heated. Even though the amount of airborne radon from water is typically less than what enters from soil gas, it can still contribute to the overall radon exposure in a home.
What Areas of the USA Have Radon?
Radon is found throughout the United States, but concentrations vary widely based on local geology. The EPA has divided the country into three Radon Zones:
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Zone 1: High potential (average indoor radon levels >4 picocuries per liter, or pCi/L)
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Zone 2: Moderate potential (2–4 pCi/L)
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Zone 3: Low potential (<2 pCi/L)
Source: EPA
States with particularly high radon levels include Pennsylvania, Iowa, Ohio, Colorado, and parts of the Appalachian region. In these areas, both soil gas and groundwater radon levels tend to be elevated due to the prevalence of uranium-rich bedrock. However, elevated radon levels have been detected in every state, and localized conditions can result in high readings even in areas classified as lower risk.
For groundwater, radon concentrations tend to be highest in areas with granite, schist, and shale formations. This includes parts of New England, the Rocky Mountains, and the Appalachian range. Private well users in these regions are particularly encouraged to test their water for radon, especially if they live in a Radon Zone 1 area.
What Are the Risks of Ingesting Radon?
The primary health risk from radon is from inhalation, but ingesting radon through drinking water can also pose a health risk—particularly for the stomach. According to the National Academy of Sciences, there is a small but measurable increase in the risk of stomach cancer from consuming water that contains high levels of radon.
That said, the EPA estimates that the majority of the cancer risk associated with radon in water comes from the gas being released into the air, not from ingestion. For example, showering with radon-laced water can increase indoor air radon levels, which in turn can be inhaled. The EPA calculates that, on average, every 10,000 pCi/L of radon in water will contribute approximately 1 pCi/L to the indoor air level.
Still, long-term consumption of radon in water—especially at levels above 4,000 pCi/L—may contribute to internal organ exposure. For people using private wells, regular testing and possible treatment is an important step toward reducing overall radon exposure.
Does Local Water Treatment Test for Radon?
In most cases, public water systems are not required to test for radon unless specifically mandated by state law. The EPA proposed a radon rule in 1999, but it has not been finalized. As a result, federal regulation of radon in drinking water remains limited, though some states (like Maine and Massachusetts) have their own testing or disclosure requirements.
Public water systems that use surface water typically have low radon levels and are not considered a major risk. Systems that rely on groundwater sources may conduct periodic radon testing, especially if the region is known for elevated radon levels.
For private well owners, testing for radon is not required by federal law, and it is not usually included in standard water quality tests. This means that unless homeowners take the initiative to test for radon themselves, they may not know whether it’s present in their drinking water.
If you’re buying or selling a home with a private well, some states or mortgage lenders may require radon water testing as part of the home inspection process. Still, it’s largely up to the individual homeowner to ensure testing is done and any issues are addressed.
How Do I Know If There Is Radon In My Well Water?
The only way to know if radon is in your well water is to test it. Radon water testing is straightforward and relatively inexpensive, especially when compared to the potential health consequences of long-term exposure.
There are two main types of tests:
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Short-term grab samples: Water is collected in a sealed container and sent to a certified laboratory for analysis. This provides a snapshot of the radon concentration at the time of sampling.
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Long-term integrated samples: A more advanced method that collects data over time, providing a better average of the radon level.
You can purchase radon-in-water test kits online or through state environmental agencies. Many certified laboratories provide detailed instructions and return shipping for sample analysis. Some areas also have radon professionals who can collect and analyze samples on your behalf.
The EPA recommends taking action if your water radon level is 4,000 pCi/L or higher. If your level is between 300 and 4,000 pCi/L, you may still want to reduce it, especially if your indoor air radon levels are also elevated.
How to Remove Radon in Water
If radon is detected in your water supply, there are effective treatment options available to reduce or eliminate it. The two primary treatment systems are:
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Aeration Systems: These systems expose water to air and then vent the radon gas safely outside the home. They are the most effective option and can remove up to 99% of radon from water. Aeration systems are typically installed where the water line enters the home.
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Granular Activated Carbon (GAC) Filters: These filters trap radon on activated carbon as water passes through. While effective for moderate levels of radon (under 10,000 pCi/L), they may require regular maintenance and can accumulate radioactive material over time. Disposal of used filters must be handled with care.
Pure Water Distillers include an activated carbon filter. After water is distilled, it passes through the post-carbon filter to remove contaminants that are not removed by distillation. With this dual process, Pure Water Distillers remove over 99.9% of harmful contaminants from drinking water. See our independently verified lab results!
It’s also worth noting that treating water does not address radon that may be entering your home through soil gas. If you have both air and water radon issues, a dual approach may be necessary.
Radon: A Hidden Danger
Radon is a hidden danger that many homeowners overlook—especially when it comes to their water supply. As a naturally occurring radioactive gas, radon can dissolve into groundwater and enter homes through private wells. While radon in air poses the greatest health risk, ingesting it through drinking water can also contribute to cancer risk over time.
High radon levels are most common in certain geological areas, including parts of the Northeast, Midwest, and Mountain West. Private well users in these regions should prioritize radon testing, as standard water quality tests do not usually include it. Public water systems may not test for radon unless required by local laws, so it’s important to ask or test independently.
Fortunately, reliable testing and treatment options are available. Whether you use an aeration system or a carbon filter, you can significantly reduce your exposure and protect your family’s health.
If you rely on well water and live in an area known for high radon levels, don’t wait for symptoms to appear—radon exposure is a silent risk. Regular testing and proactive treatment can give you peace of mind.
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