The thesis paper focused on the water supply network of Addis Ababa, capital city ofrnEthiopia. The Addis Ababa water supply has three subsystems according to its principalrnwater supply sources. These are Akaki, Gefersa and Legedadi subsystem. The paperrnconsidered the legedadi subsystem.rnThe main objective of this study is to improve the legedadi water supply distributionrnservice system and control its operation with the aid of computer analysis.rnTo analyze and improve the existing water distribution system, a model was developedrnutilizing Water CAD software. The model can be used to solve ongoing problems,rnanalyze proposed operational changes, and prepare for unusual events. By comparingrnmodel results with field operations, the operator can determine the cause of problemsrnin the system and formulate solutions that will work correctly the first time.rnThe model run was performed for different scenarios to analyze the system model, whatrnif conditions. These scenarios are at average day demand, FCV-66, FCV-71, FCV-72, andrnFCV-73 set closed, FCV-73 set closed and firefighting flow.rnComparing representative samples of the distribution mainâ€™s pressure field-test withrnthe model-simulated values showed a reasonable and small difference to calibrate thernmodel.rnThe model analysis result showed the different problems of the system. These are agedrnpipes, oversized and undersized pipes, and high pressures.rnThe system has been modified using the design criteria of velocity and pressure. Highrnpressures in the existing system caused by customers at too low demand have beenrnidentified and solution is established using pressure-reducing valves.rnFinally, 10% of the total distribution mains are modified and 19.81% of the distributionrnmains are old enough, replaced with newer one. These modifications improved thernperformance of the system and saving 5,081m3/day amount of water leakage.rnHydraulic Network Modeling and Upgrading of Legedadi Subsystem Water supply