Sustainability assessment is one of the critical issues for any urban water supply system and it is included in the second growth transformation plan of Ethiopia. Intermittent water supply, drinking water shortages, and water quality issues are familiar problems in Debre Tabor town. Thus, the main focus of the present study was evaluation of the sustainability of the water supply system in Debre Tabor town based on hydraulic efficiency of the existing distribution system, water quality analysis, and customer satisfaction in terms of quality and quantity. To achieve this objective, relevant data was gathered from both primary and secondary sources. The sustainability of the urban water distribution systems was measured by the sustainability index (SI) based upon reliability, resiliency, and vulnerability as performance signifying criteria. According to the findings of the study, the sustainability index of the distribution system was 0.37, which indicated that the system was not sustainable. The water quality index (WQI) based analysis results showed that 55.5% of the samples from boreholes and reservoirs and only 45% of the samples from tap waters were very good for drinking purpose. The average WQI in the boreholes and reservoirs was 98, which showed a "good" water supply for drinking purposes as per both the WHO and Ethiopian drinking water standards. However, the tap water was below this. On the other hand, the town's average per capita consumption and water loss were 11.87liters/day, and 24%, respectively. Generally, the findings of the study disclosed that the sustainability of the town's water supply system is mainly affected by social, economic, environmental and technical conditions. The study suggests water supply problems to be addressed by conserving water sources, using additional alternative sources of clean water, and working on activities of limiting water loss. Keywords: Reliability, Resiliency, Sustainability, Sustainability indicators, vulnerability, Debre Tabor