Radon, a cancer causing radioactive gas, can be present in both air and water
Radon occurs naturally in soil and groundwater as a gas that you cannot smell, see or taste. Radon can seep up through the cracks in basements or floors, or through water use such as bathing. Lung cancer is the greatest concern from elevated levels of radon, and ingesting radon presents a risk of stomach cancer. The only way to be sure if a building has high levels of radon is to test using a radon measurement device.
U.S. EPA Recommends Testing
Test your home for radon.
Fix your home if your radon level is 4 picocuries per liter, or pCi/L, or higher.
Radon levels less than 4 pCi/L still pose a risk, and in many cases may be reduced.
Radon testing is required for most property sales. If your building has high levels, it should be tested annually. Buildings with high levels can have radon mitigation systems installed.