The 1993 Cryptosporidium illness outbreak in Milwaukee, Wisconsin and the more recent E. coli tragedy in Walkerton, Canada underline the need for water utilities to establish and maintain effective partnerships with local public health and emergency planning agencies. In San Antonio, Texas local water utilities working with their Local Emergency Planning Committee (LEPC) were able to participate in a simulated waterborne illness outbreak and tabletop exercise with local public health professionals and regulatory agency officials. This paper reports how a simulated disease outbreak, "Don't Drink the Water", was designed as a training exercise to introduce water and reuse water operators to basic epidemiological techniques used by public health officials in the investigation of a suspected waterborne illness outbreak. Working in teams, participants were provided information on individuals experiencing symptoms of a waterborne illness. Each team included water operators, public health sanitarians and regulatory agency professionals. Participants used data from patient histories to construct an epidemiological curve to approximate the time of exposure and to identify the most likely source of the illness as a picnic. Using basic epidemiological techniques to calculate specific food and beverage attack rates, it was possible to eliminate contaminated water as the cause of the illness and to identify shrimp consumed during a picnic as the probable source.