For a two-year period, the states of Colorado, Vermont and Washington tested the effectiveness of seven surveillance methods for identifying waterborne disease outbreaks. Six of the methods were termed active and utilized procedures soliciting reports of illness. The seventh method was termed passive and was the traditional waterborne disease surveillance method, which relies upon voluntary reporting of illness, used by all three states prior to the study. For the purpose of this study, passive surveillance was enhanced through publicity and communication with the public health profession to encourage the voluntary reporting of illness. One waterborne disease outbreak was identified through use of the six active methods while 16 were reported through enhanced passive surveillance. The 17 outbreaks represented a 20% increase in occurrence over a two-year period prior to the study.