The primary goal of this study is to review the hydraulic performance of the existing distributionrnsystem of the city, Addis Ababa, Legedadi subsystem which is aimed to help the city understand itsrndistribution system needs and assist them in long-term planning of water assets.rnThe scope of the study is to evaluate the performance of the existing drinking water distributionrnsystem using hydraulic simulation software in integration with GIS, and recommends the possiblernremedies to improve the efficiency of the existing system.rnThe hydraulic simulation software used for this study is Water CAD V8i distributed by BentleyrnSystems. Bentley Water CAD V8i was selected due to ease of model building and operation and itsrngreater programming capabilities as compared to EPAnet.rnHydraulic modeling of the system is performed by considering the system as a continuous supplyrnsystem, and the evaluation process adopted the Extended Period Simulation method. The systemrnhas been checked for different scenarios and alternatives to deepen our investigation. Considering,rnthe model is calibrated at specific locations and the results with field measurements showrnreasonable difference, so that we use some fine tuning using Hazen Williams C â€“value to alignrnwith the field data.rnAs a matter of fact, I have proved that, there is hydraulic inefficiency in the existing water systemrnto serve the city (Legedadi sub system) and to cope with the future demand.rnThe outputs show that the network is exposed to relatively high and low values of pressure andrnvelocity, which have negative effects on the performance of the network as well as in the waterrnquality of the system. Besides, failure is forecasted in considering the age of pipes for reinstallationrnand maintenance. As a result, Pipes with ages more than 30 years are replaced andrnover and under sized pipes have been re-sized. Consequently, the Hazen Williams C-value hasrnbeen totally improved and it enhances the system performance.rnThe evaluation study of the water hammer in the Addis Ababa distribution system, which has beenrnimplemented to investigate the effects of this phenomena shows that the water hammer valuesrnincrease by increasing the velocity of water in pipes, and the values of shock pressures were withinrnthe limits of the shock pressures in water pipes systems.rnIn the study, the major hydraulic parameters, the variations, and the relations between them andrnother factors, which control the performance of the water supply networks are considered andrndiscussed in detail during analysis.rnTo this end, the network is assessed and possible corrections are given for Optimum water supplyrnnetwork even using Darwin Optimum Pipe Network Designer tool so as to at least the system meetrnthe required design criterion as a constraints. Moreover, the Legedadi subsystem has beenrncategorized for 14 optimum Pressure zones with their corresponding Reservoirs (Pumpingrnstations).