Accidental spills, vandalism, and acts of terrorism have become a growing threat to the safety and security of public water utilities in the United States and abroad. Adequate plans to safeguard supplies include design of facilities with security as a priority and training personnel to recognize and correct potential breaches in security. Two municipal water supply systems in the Pacific Northwest were evaluated in this study to determine the degree of safety and security provided to discourage, detect, and counteract accidental or intentional contamination of their raw and treated water. One is a groundwater system; the other is supplied by surface water. The findings will help increase awareness of the problems confronting utility personnel, regulatory agencies, and design engineers. Includes 14 references, figures.