The City of London (Population 336,000p) water supply and distribution system is approximately 1,500 kilometers in length. The system includes one 47 km supply line from Lake Huron (328 MLD peak capacity) and one 29 km supply from Lake Erie (22.7 MLD). Storage capacity is provided by the Arva (109 ML) and Springbank (208.5 ML) reservoirs. The City's water system is subdivided into two pressure zones (high and low). London maintains a state-of-the-art ARCINFO Geographic Information System (GIS). In addition, a SCADA system continuously provides the City with pressure and flow information at key points of its water network. To fully realize the engineering potential of its investment in the GIS and SCADA systems, the City implemented a carefully planned water modeling effort staged in two phases. Our paper reports on the methodologies used for: model selection; demand analysis and demand allocation; SCADA integration; and model calibration including use of the Inverse Transient Methodology for calibration of the model. Phase 1 of the project provided the City of London with a skeletonized network model of its primary watermains and facilities, which can be readily interfaced with the City's GIS and SCADA systems and grown through future system additions. This has already occurred to some extent to facilitate growth planning. The developed master model will serve as the basis for implementation of the second phase of the project involving sub-model development for the City's overall distribution network.