Radionuclides are radioactive health-effect contaminants. The eSpring™ Water System is the first NSF certified system to reduce radon and radon decay products in drinking water. Radon is a naturally occurring radioactive gas that has no taste, odor, or color. Radon is produced by the natural decay of uranium found in soil and rocks containing uranium ores, granite, shale, phosphate, and pitchblende. Most radon rises out of rock and is harmlessly dissipated in the atmosphere. However, radon gas can accumulate and dissolve in underground water sources such as wells.