Radon can be found in ground water sources of drinking water (rather than surface waters, such as rivers, lakes and streams) in some parts of the United States. Radon is a naturally occurring radioactive breakdown product of uranium that can dissolve and accumulate in ground water. However, the primary source of human exposure to radon is breathing radon in indoor air of homes. Most of the risk from radon in drinking water (nearly 90 percent) comes from breathing radon released to indoor air from household water uses.
The most effective treatment is to remove radon from the water before it enters the home. This is called point-of-entry treatment. Treatment at your water tap is called point-of-use treatment.
There are no laboratories certified to perform radon in water analysis and no standard for radon in water, whether for private wells or community water systems.
It is estimated that about 10,000 pCi/L of radon in water will raise the radon levels in air by 1 pCi/L when the water is aerosolized, for example, by showering. This called a transfer coefficient and is 10,000:1 for radon. Inhalation of radon is the primary route of radiation exposure to humans.
See EPA’s web site for additional information on radon in drinking water: http://water.epa.gov/lawsregs/rulesregs/sdwa/radon/regulations.cfm
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