What is it?
Radon in well water is the same invisible radioactive gas that can seep out of the ground into the air of a house. Since water wells are drilled deep into water-bearing rock, the water absorbs radon if radon is present in that rock.
What is wrong with it?
When you use water (particularly for showering), the radon is released into the air. Breathing the radon is unhealthy, as described in the Radon In Air post.
What do I do now?
Have the well water tested for radon by a lab. Most home inspectors can administer this for you. While radon in the well water itself should not vary widely over time, there is always some variation in testing. This is because radon gas easily escapes water and some is lost even during careful sampling.
If the radon level in the well water is elevated, there are reliable treatment systems available to eliminate it. A more detailed discussion of what constitutes “elevated” is available in a document titled “Radon in Air Interpretation” available on the Reference Information page.
What do I do when I own the house?
Live normally and enjoy the home.
While theoretically, the radon level in the well water should not change systematically over time, it might be best to retest every few years just to be sure.
If you have a radon in well water reduction system, have it serviced from time to time, consistent with the recommendations of the installer.