Geographic information systems (GIS) have been around for decades, but only in the past 10 years or so has technology been developed that makes GIS useful to the mainstream needs of water utilities and public works departments. This article provides examples of how utilities in Canada, the United States, and Australia are using GIS to manage and maintain their water distribution networks and provides information about how GIS can be used to analyze the data collected during a water main corrosion study. The authors use the results of a geographic analysis of the data collected during a study of Toronto, Ontario's cast-iron water mains to begin to quantify their risk for deterioration. The study results also provide new information regarding the relationship between soil properties and the external corrosion of cast-iron water mains. Includes 8 references, table, figures.