A hydraulic model has been developed for the Pinellas County Drinking Water System, a large and complex water transmission and distribution network including six pumping stations, 11 storage tanks, approximately 2,000 miles of piping, and thousands of valves. The piping network was created from GIS-based shapefiles of the system and corrected using record drawings. The elevations were assigned to the network nodes using 1-foot contours of a County-wide Airborne Laser Swath Mapping. The Hazen-Williams coefficients were assigned based on known pipe materials and diameters with adjustments for age and expected flow velocity. Monthly retail meter records, real-time wholesale meter records, and unaccounted-for water flows were allocated to the nodes using the conventional bottom-up approach. Boundary conditions were incorporated into the model. Anomalies were identified and corrected. The model was calibrated using the testing data for the maximum hour demand. The simulation results were compared with the testing results for six other demand events. The model was in close agreement with the physical system in all simulation scenarios. The authors have successfully used the model in the design of a 110-MGD water blending facility. Includes 7 references, tables, figures.