Radon
Radon in Water
Radon can also enter homes through their water systems. Water in rivers and reservoirs usually contains very little radon, because it escapes into the air; so homes that rely on surface water usually do not have a radon problem from their water. Large municipal water systems processes include aerating the water, which allows radon to escape, and also delays the use of water until most of the remaining radon has decayed.
Small public water works and private domestic wells often have closed systems and short transit times that do not remove radon from the water or permit it to decay. The radon escapes from the water to the indoor air as people take showers, wash clothes or dishes, or otherwise use water. Breathing the radon in the air increases the risk of lung cancer.
Research suggests that swallowing water with high radon levels may pose risks, too, but these risks are believed to be much lower than from breathing air containing radon. Compared to radon entering the home through soil, radon entering the home through water will in most cases be a small source of risk.
The areas most likely to have problems with radon in ground water are areas that have high levels of uranium in the underlying rocks. For example, granites in various parts of the United States have resulted in high levels of radon in ground water.