Prior to World War II, interest in the radioactivity of water was nonexistent except for the possible exploitation of such water for bathing or drinking. Fortunately, a few investigators were sufficiently interested in the phenomenon of natural radioactivity to pursue serious studies so that some information was accumulated on radioactive waters (16). This work has proved helpful because it focused attention on the exceedingly small amounts of materials involved and led to the development of methods suitable for their measurement.