Sustainability assessment is one of the critical issues for urban water supply system and it is included in the second growth transformation plan of Ethiopia. Recently Bahir Dar city has passed through various social and economic progresses. However, the city has problems such as intermittent water supply, hygiene and linkages for providing sustainable water supply system to the city. These leads to demands for the expansion and improvement of basic water supply services. Therefore to satisfy the basic water supply services, sustainability of water supply system is found to be important. This study focuses on sustainability assessment of urban water supply system of Bahir Dar city based on accessibility, customer satisfactions, water availability and Hydraulic efficiency of the distribution system. To achieve its objective relevant data were gathered from both primary and secondary sources. The collected qualitative and quantitative data were organized and analyzed using the Statistical Program for Social Science (SPSS), Microsoft Excel, WaterCADv8i and ArcGIS tools. The hydraulic efficiency of the distribution system is also measured by sustainability index (SI) using reliability, resiliency and vulnerability performance criteria. The result of this study indicates that the average domestic per-capita consumption and water loss of the city was 46.13 l/c/day and 58.4 % respectively. The current and future water stress index, which is considered in the year 2017, was 685 m3/c/year, 809 m3/c/year in 2020, 671 m3/c/year and 575 m3/c/year in the year 2025 and 2030 respectively. The average score of accessibility in terms of distance and time to collect water is found to be 30.54 %, customer satisfaction in terms of quality and quantity of drinking water service is 19.98 % and 20.95 % respectively. The score of the affordability to pay is also calculated as 28.54 %. Regarding to these score only 54 % of urban water supply is sustainable. The reliability, resiliency and vulnerability for both velocity and pressure were 0.65 and 0.33, 1.89 and 0.53 and 0.35 and 0.43 respectively. These results revealed that the sustainability index of the distribution network is 0.695. Generally, the sustainability problem of the urban water supply system is majorly influenced by social and environmental factors.