Radon gas can also enter homes through the water supply. Radon dissolves and builds up in water from underground sources, such as wells. The radon in your water can enter the air in your home when you use water for household activities such as showering, washing clothes and cooking. For every 10,000 picocuries per liter (pCi/L) of radon in your water, it is estimated that 1 pCi/L is added to your radon in the air. If your water comes from a lake, river, or reservoir (surface water), radon is not a concern. The radon is released into the air before it reaches your home. Some states like Connecticut, New Hampshire and Vermont recommend fixing radon in water if the levels are above 5000 pCi/L.
The North Carolina Radon Program recommends a radon-in-water advisory be set at two levels. At the moderate level, concentrations between 4,000 and 10,000 pCi/L in water, treatment is considered optional. At the elevated level, concentrations at or above 10,000 pCi/L in water, treatment should be considered in conjunction with the treatment of indoor air radon released from soil gas. In most cases, mitigation of soil gas radon will have the greatest impact on reducing overall radon exposure and will usually take precedence over treatment of radon in water.
Some radon stays in the water. Radon in the water you drink can also contribute to a very small increase in your risk of stomach cancer. However this risk is almost insignificant compared to your risk of lung cancer from radon.
It is suggested by the EPA that if you have elevated air radon levels and are on a private well, you should have your water radon tested.
Removal of Radon from Water
There are only two practical techniques for removing radon from water in a residential setting. One technique uses activated carbon. The carbon adsorbs the radon from the water. The radon then finishes decaying in the carbon. Activated carbon should only be used if the radon water levels are below 5000 pCi/L. This low level is recommended by the EPA because of the concern over the buildup of radioactivity.
Aeration systems are is used on very high levels of radon. The radon is released from the water by bubbling air through the water. The radon is then vented to the outdoors. There is no buildup of radioactive materials when this technique is used. The removal of well over 99% of the radon from the water can be achieved with these units. These units do require the repressurization of the water after it is treated and care must be taken to properly vent the gas. This venting should be done above the roof line just like an air radon system and there should always be an auxiliary fan outside of the living space to provide for the save removal of the gas. Water aeration is considered by the U.S. EPA to be the best available technology for removing radon from well water. Unlike other methods, such as granular activated carbon tanks, aeration does not pose the threat of waste buildup.