By far, the greatest risk to health from radon occurs when the gas enters the house from underlying soil and is inhaled. The U.S. Environmental Protection Agency (EPA) is studying ways to reduce radon in houses, including methods to remove the gas from water to prevent its release in houses when the water is used. While this research has not answered all the questions about household water treatment systems, current information that may be of immediate use to homeowners is available. This booklet is intended specifically for homeowners who suspect that the water they get from their own well, or water they receive from a water utility that uses well water, may be a significant source of radon in their homes. Discussions include sources of radon in water, testing for radon in water, control methods such as the granular activated carbon filter, and costs associated with radon control. EPA regional offices and state radon contacts are listed. (CW)