The purpose of this paper is to test and illustrate the application of anintegrated approach to the control of coliforms in the water distribution systemof the City of Laval, Quebec, Canada. This system serves about 300,000 consumersusing three water treatment plants. Treatment trains at two of these plantsconsist of dual media sand and anthracite filtration, ozonation, andchlorination. The other plant includes dynamic settling, rapid filtration,ozonation, biological activated carbon (BAC) filtration, and chlorine dioxidedisinfection. The hydraulic functioning of the system has been modeled with theEPANET software. A fairly complete database, related to quality parameters andinterventions (that include pipe leaks and breaks, flushing, hydrants, and pipeinstallation and rehabilitation) has been collected. The water quality impact of suchinterventions has been studied and is presented as two case studies. Includes 15 references, figures.