An analysis of statistics compiled on outbreaks of waterborne disease from 1946 to 1980 and from 1965 to 1982 showed that disinfection was not provided where it was needed and was not properly operated where it was provided. Chlorine concentration, contact time, pH, temperature, and interfering substances all must be evaluated to determine disinfection requirements. Use of reliable chlorination facilities and proper application of current technology can control and prevent waterborne diseases.