In Addis Ababa, Ethiopia, open reservoirs provide the majority of the drinking water. In the study present and future condition of these water sources and supplies were systematically assessed regarding water quantities. The study was done by reviewing municipal documents and accessing meteorological, hydrological and demographical data in Addis Ababa. 0%, 5% and 10% change in reservoir inflow/rainfall were used and projections for 2020 and 2030 were used to estimate future temperature and population sizes. The result indicated that supplied water quantity per capita from surface sources in Addis Ababa is likely to be reduced. Both climate and socio-economic related vulnerabilities were identified and the four following got the highest risk score: Increases in population, increased per capita water demand, overexploited land and increased distribution losses.At present the annual increase in population in Ethiopia is 4.4% and annual GDP increase is 7%, leading to a growing water demand in Addis Ababa. If the water supplies are not substantially increased the situation will lead to water scarcity. By 2020 water demand coverage will be 34% and by 2030 22%, compared with the current 50% coverage.Overexploited land was also identified as a major vulnerability due to the impact on catchment hydrology and distribution losses, caused by insufficient maintenance and replacement of aged pipes. At present 20% of the treated water is lost and it is likely to increase during the coming decades. However, the climate change induced rainfall variability is unlikely to cause large problems within the observed timeframe. Even with a 100 year drought 14% of the available water would be spill due to the limited reservoir capacity.To secure future water distribution Addis Ababa Water and Sewerage Authority (AAWSA) should build dams north of the Entoto ridge. They should also gain further understanding about and find appropriate measures for, highlighted vulnerabilities. A full vulnerability assessment should be done by AAWSA and they should consider implementing a „Water Safety Plan‟ for the whole water supply system.