Radon is a radioactive gas produced by the decay of uranium found in rock and soil. Exposure to radon is a known human carcinogen, classified alongside substances like tobacco smoke and asbestos. While the gas is most commonly associated with seeping directly from the soil into a home’s air, water drawn from underground sources can also carry the gas. Understanding this water-to-air pathway is necessary for managing the overall risk of exposure within the home environment.
How Waterborne Radon Enters the Home Environment
Radon dissolves readily into groundwater, making private wells that draw from underground aquifers the most common source of waterborne contamination. As the water travels through uranium-rich rock formations, it absorbs the gas before being pumped into the household plumbing system. In contrast, public water supplies sourced from surface water, such as reservoirs and rivers, typically release most of the dissolved radon into the atmosphere before the water reaches the treatment plant.
The primary danger from waterborne radon occurs when the gas escapes the water and enters the indoor air. Common household activities that agitate water, such as showering, washing dishes, and doing laundry, accelerate this process of volatilization. This aeration releases the trapped radon gas into the breathing space of the home, contributing to the overall indoor air concentration. This means the greatest risk from contaminated water is not from drinking it, but from inhaling the gas released during its use.
The Distinct Health Risks Associated with Radon Exposure
The most significant health risk from radon, regardless of whether it originates from soil or water, is the inhalation of the gas and its decay products. Once inhaled, radon rapidly decays into tiny, solid radioactive particles, including polonium and lead. These decay products can attach to dust particles and become lodged in the cells lining the lungs, where they emit radiation.
Over time, this radiation damages the lung tissue, leading to an increased risk of lung cancer. The U.S. Environmental Protection Agency (EPA) estimates that radon is the second leading cause of lung cancer, responsible for thousands of deaths annually. The risk is particularly elevated for smokers, who face a higher chance of developing lung cancer due to the synergistic effect of both exposures.
Ingesting radon through drinking water presents a separate health concern. When contaminated water is swallowed, the radon is exposed to the digestive tract. This ingestion is linked to a risk of stomach cancer. However, the EPA estimates that the risk of lung cancer from inhaling radon released by water is substantially greater than the risk of stomach cancer from ingesting the water itself.
Testing Your Water for Radon Concentration
Testing for radon in water is recommended for homes that use a private well supply, as municipal water systems are often monitored and treated. The initial priority should always be to test the indoor air for radon, as this represents the greatest health hazard. If air testing reveals an elevated level, water testing can help determine if the well is a contributing source.
Water samples must be analyzed by a certified laboratory to measure the concentration in picocuries per liter (pCi/L). While there is no current federal standard for radon in private well water, action levels are often suggested by state and local authorities. A common guide suggests that 10,000 pCi/L of radon in water contributes approximately 1 pCi/L to the indoor air concentration. Some experts recommend considering water treatment if concentrations exceed 4,000 pCi/L, especially if air levels are also high.
Proven Methods for Water Radon Mitigation
When testing confirms that water is a significant source of radon, two primary methods are employed to remove the gas before it enters the home’s plumbing. Aeration treatment can remove up to 99% of the dissolved radon. This system works by agitating the water with air, causing the radon to escape the liquid phase. The radon-rich air is then safely vented to the outside atmosphere, preventing its release indoors.
Granular Activated Carbon (GAC) filtration is the second common method. In this system, water passes through a bed of carbon material that adsorbs the radon gas. GAC filters are simpler and require no electricity to operate, making them a practical choice for moderate or low concentrations. However, GAC is less suitable for extremely high radon levels because the radioactive material accumulates within the filter bed, requiring careful handling and disposal of the spent filter media.