Sources of radon in drinking water
Radon is a radioactive gas. It occurs naturally and is produced by the radioactive decay and breakdown of uranium in soil, rock, and water. It can also dissolve into our water supply. The radioactivity emitted from uranium in the aquifer forms radon gas, soluble in water and also readily transported through the aquifer in the gas phase.
As radon gas moves through the subsurface, it can also dissolve and accumulate in groundwater and affect drinking water supplies. Radon gas easily escapes from water once the water is exposed to air. Radon gas is released into the indoor air of a home by simply running the water for household purposes, such as for the shower, washing dishes, and laundering.
While the risk of radon entering homes through drinking water is small compared with that of radon entering through the soil, the gas released from the water will contribute to the total indoor air concentration. The EPA estimates that about 1-2 percent of the radon in indoor air comes from drinking water.
Radon gas is also found in igneous rocks (such as granite) and hydrothermal rock veins. Some hot springs are known for their naturally occurring radioactivity due to radon.
Radon cannot be detected by taste, sight, or smell. The only way to know the concentration is through sampling and testing.
Potential health effects of radon in drinking water
Radon is a radioactive gas occurring naturally in the environment. It is produced by the breakdown of uranium in soil and rock. Radon gas, moving through the soil, enters buildings through cracks and holes in the foundation. Drinking water that has high levels of radon may be a health risk, but breathing air high in radon concentration is more harmful to your health.
The health effects of radon exposure are chronic (the delayed result of continuous consumption over a long period of time) rather than acute (the immediate result of consumption). Individual risk depends on the concentration, how much water was consumed and for how long, as well as the age and general health of the individual.
Testing for radon in drinking water
The quality of water supplied by public water systems is regulated by the U.S. Environmental Protection Agency (EPA) under the federal [Safe Drinking Water Act. If users of public water supplies want information regarding their water supply, they can contact their water supplier.
If users want to know the concentration of radon in a private water supply, they must have the water tested by a state certified laboratory.
Options for radon in drinking water
Public community water supplies must provide drinking water that is in compliance with the maximum contaminant level allowed by the Environmental Protection Agency. The EPA is currently proposing standards for radon in drinking water.
The proposed standards will apply only to community water systems that regularly serve 25 or more people and that use groundwater or mixed ground and surface water. They will not apply to systems that rely on surface water where radon levels in the water are very low. The proposal will provide states flexibility in how to limit exposure to radon by allowing them to focus their efforts on the greatest radon risks (those in indoor air) while also reducing the risks from radon in drinking water.
- First Option - States can choose to develop enhanced state programs to address the health risks from radon in indoor air, known as Multimedia Mitigation (MMM) programs, while individual water systems reduce radon levels in drinking water to 4,000 pCi/L or lower (picoCuries per liter, a standard unit of radiation). The EPA is encouraging states to adopt this option because it is the most cost-effective way to achieve the greatest radon risk reduction.
- Second Option - If a state chooses not to develop an MMM program, individual water systems in that state would be required to either reduce radon in their system's drinking water to 300 pCi/L or develop individual local MMM programs and reduce levels in drinking water to 4000 pCi/L. Water systems already at or below 300 pCi/L standard would not be required to treat their water for radon.
See the EPA's Proposed Radon in Drinking Water Regulation to track the latest information on this contaminant.
Private water supply users wishing to reduce radon concentrations can consider granular activated carbon filtration or aeration. Each method has advantages and disadvantages, which must be considered prior to making a decision.