Where and how does radon get into drinking water?

Radon in drinking water is a significant health hazard, though a lesser hazard than radon in indoor air. Homes supplied with drinking water from a private well, and community water systems that use wells as water sources have a greater risk of exposure to radon in water.

Radon in water is found in nearly all sources of surface water and groundwater. It is created by the radioactive decay of radium, a naturally occurring radioactive element found in underground rock formations, particularly granite and quartz. Water that flows through or over radium-rich rock formations accumulates radium and, thus, radon resulting from the decay process.

Groundwater typically has much higher levels of radon than surface water. This is because radon in groundwater is trapped by being submerged underground and it cannot easily escape. Because of this, water supplies from underground wells have a much higher probability of having significant levels of radon. Drinking water originating from a surface-water source is probably not a significant health hazard for radon in water. Large, pre-treated municipal water supplies typically have negligible levels of radon in water because this type of water supply is usually drawn from surface- water sources, and because water treatment tends to reduce radon levels even further.

Property owners with wells who have confirmed elevated radon levels in the indoor air should also test their well water for radon. Radon in the water supply can increase the indoor radon levels, although radon entering the home through water will be a small source of risk compared to the levels of radon entering through the soil. The EPA estimates that indoor radon levels will increase by about 1 pCi/L for every 10,000 pCi/L of radon in the water. (The EPA’s Office of Ground Water and Drinking Water has developed publications related to radon in drinking water that can be found online at www.epa.gov/radon/rnwater.html

What are the risks of radon exposure?

Radon’s primary public health risk is by breathing in the indoor air of homes. This contributes to about 20,000 lung cancer deaths each year in the United States, according to the 1999 landmark BEIR VI Report by the NAS on radon in indoor air. Radon is the second leading cause of lung cancer in the U.S. Based on a second NAS report on radon in drinking water, the EPA estimates that it causes about 168 cancer deaths per year: 89% from lung cancer caused by breathing radon released from water; and 11% from stomach cancer caused by drinking radon-contaminated water.

Drinking water that has high levels of radon may be a health risk, but breathing air high in radon concentration is more harmful. Breathing in radon gas over a long period of time can increase the risk of lung cancer. Drinking water contaminated by radon may increase the chances of developing stomach cancer.

While most radon-related deaths are due to radon gas accumulated in houses from seepage through cracks in the foundation, up to 1,800 deaths per year are attributed to radon from household water. Showering, washing dishes, and doing laundry can disturb the water and release radon gas into the breathable air.

As with radon in the indoor air, the only way to be certain of whether there is radon at actionable levels in the home’s water supply is to test it.

How is radon in water tested?

Before testing for radon in the residential water supply, test the air. If the indoor air’s radon level is high and the home uses groundwater, test the water. If the radon level in the air is low, there is no need to test the water.

For waterborne radon, a simple step to ensure reduced radon levels is to make sure that the bathroom, laundry room, and kitchen are well ventilated. If the well water has only moderate levels of radon, this may adequately reduce exposure to waterborne radon. However, if the well has high levels of radon, consider using water-treatment devices, such as granular activated carbon (GAC) units and home aerators.

What do the results of a water test mean?

Test results are expressed in picocuries of radon per liter of water (pCi/L). In general, 10,000 pCi/L of radon in water contributes roughly 1 pCi/L of airborne radon throughout the house. The EPA advises consumers to take action if the total household air level is above 4 pCi/L.

It is possible to estimate how much the radon in the water supply is affecting the indoor radon level. The formula to gauge whether indoor air levels are elevated is to subtract 1 pCi/L from the indoor air radon level for every 10,000 pCi/L of radon that was found in the water. For example, if there are 30,000 pCi/L of radon in the water, then 3 pCi/L of the indoor measurement may have come from radon in the water.

If most of the radon is not coming from the water, mitigate the indoor levels and then re-test the indoor air to make sure that the source of elevated radon was not coming from the property’s well. If a large contribution of the radon in the house is coming from the water supply, the homeowner should consider installing a special water treatment system to remove the radon. The EPA recommends installing a water treatment system only when there is a radon problem found in the water supply.

What should I do if I have concerns about radon exposure?

The 1996 Safe Drinking Water Act Amendments required the EPA to establish several new health-based drinking water regulations, including a multimedia approach to address the public health risks of radon exposure.

Consult a healthcare provider to discuss your concerns, and consider using one of the two methods for removing radon from water: aeration treatment or GAC treatment. These methods are discussed in the next section. For more information, read the How to Perform Radon Inspections Book.