What is a significant source of radon entry into homes besides the foundation?

Well water serves as a significant source of radon entry into homes because radon can dissolve in water or be released into the air from water supplies, especially when the water is used for showers, baths, or dishes. When the water is agitated, radon gas can escape into the indoor air, contributing to the overall levels of radon present in a home.

Other sources, such as houseplants, paint materials, and insulation types, typically do not emit radon or contribute to its entry in any meaningful way compared to well water. Therefore, understanding the pathways for radon entry, including from water, is crucial for assessing and mitigating potential radon exposure in residential settings.