Hydraulic models have proven to be effective tools in the assessment and evaluation of water distribution systems. Historically, hydraulic models have relied on manual logs of system layouts, operations and billing for their input information. Consequently, time and level of effort limit the amount of information that is used in model development. With the advent of Geographic Information Systems (GIS) and electronic billing, integration of electronic information with models has resulted in cost savings, reduction in errors and the possibility of modeling large systems within reasonable timeframes. Metcalf & Eddy Inc. (M&E) recently completed a hydraulic model of the Hartford, CT Metropolitan District Commission's (MDC) water supply and distribution system. Using the District's extensive GIS database, system information was imported into MWHSoft's H2OMap® software. AutoCAD renderings of pumping stations were also incorporated into the model with detailed information on valves and piping within the stations. Information obtained from the District's electronic billing system along with GIS street information was used to geolocate customers and allocate demands accurately. Utilizing this model, M&E conducted a thorough analysis of the MDC's system and developed a program of improvements to address deficiencies in the system. In addition, the MDC now has a powerful tool to evaluate future changes within their system. Includes figures.