Ground water can be added sources of indoor radon. Although radon gas in drinking water adds a slight chance for increased stomach cancer, waterborne radon is most dangerous when used in showering, laundry, washing dishes, etc. Heating and/or agitating allows the radon to leave the water supply and enter your household air where it can be breathed into the lungs. Some parts of the country (i.e., New England, Appalachians, VA/NC/SC Piedmont, Rockies) are notorious for producing high levels of radon in well water.

Second Edition of Doug Kladder's Radon Mitigation Book. This DIY book goes through the fundamental steps in designing and installing radon mitigation systems as well as radon resistance new construction (RRNC) features.

Test your building site for radon prior to starting construction. Although the radon entering a building after it has been completed will change the dynamics of radon in the underlying soil, some clients like to determine the amount of radon naturally degassing prior to contruction. The Open Land kit can give you an idea of how much radon is coming from the top layer of the building site. It is recommended to excavate the land down to where the foundation will be constructed prior to testing.