This study focused on hydraulic performance evaluation of water supply distribution system in Atse Tewodros sub city subsystem in Bahir Dar city. To achieve the main objective both secondary and primary data were collected and hydraulic modeling software tool such as Bentley WaterGEMS, Google Earth, and Global Mapper were utilized, along with other relevant materials. To examine the distribution system, simulation runs were conducted for peak and minimum demand conditions. According to the demand calculation, which considered population, climate, and socio-economic factors, the total average daily demand was 206.13 l/s. The model calibration was performed for the distribution system, using the most sensitive parameters, including pipe roughness and nodal demand adjustment, to reduce the difference between measured and predicted flow and pressure. After calibration, the performance of the new distribution system was evaluated. At minimum demand, 5.58% of nodes had a pressure value < 15 mH2O, 93.24% of nodes had a pressure value b/n 15-70 mH2O, and 1.18% of nodes had a pressure value > 70 mH2O. At peak hour demand, 26.5% of nodes had a pressure value < 15 mH2O, and 73.5% of nodes had a pressure value b/n 15-70 mH2O. The velocity of pipe flow for new distribution system at minimum demand showed that, 83.14% of pipes had a velocity < 0.6 m/s, 16.63% of pipes had a velocity b/n 0.6 - 2 m/s and 0.23% of pipes had a velocity >2m/s. similarly at peak hour demand 56.86% of pipes had a velocity < 0.6 m/s, 40.35% of pipes had a velocity b/n 0.6 - 2 m/s and 2.79% of pipes had a velocity > 2 m/s. In general, the sub-city's water distribution system had significant problems, as evidenced by pump failures, demand calculation issues, power outages, and new system design challenges. Therefore, it is crucial to address these problems, especially pump failures and power outages Keywords: - Water demand, Hydraulic performance, WaterGEMS Model and Atse Tewodros sub city.