If an ion exchange device is added to your system, test your water after installation to make certain it is working to remove radium. Although radon concentrations in ground water are more likely to be higher in certain areas relative to others, the only way to be certain of the radon concentration in the water supplied by any given well is to have the water tested. Prediction of radon concentration at an individual well is very difficult and imprecise. A high level tested in a neighbor's water does not mean your water will also test high. In homes where high indoor radon levels are measured and where water is supplied by a privately owned well, the EPA further recommends that the well water be tested as a potential contributing source of the airborne radon.
Opinions vary with regard to levels of radon and when to take treatment action.
If a large percentage of the radon in your house is from your water, the U.S. EPA recommends that you consider installing a water treatment system to remove radon. Both homes and water supplies can be treated to reduce radon. It is impractical and unnecessary to test your water for all possible contaminants. Routine testing for a few of the most common contaminants is recommended, however. Even if you currently have a safe, pure water supply, annual testing can be valuable because it establishes a record of water quality.