Tehran has been facing water shortage challenge for decades and it has not hesitated to exploit neighboring watersheds. Rising demand and limited resources might make water crisis a strong possibility in the near future. An accurate and applied analysis of Tehran's urban water system (UWS) would be the first step to be taken to prevent such a crisis. This research is an effort to make an assessment of different aspects of urban water systems and to determine sustainability level of Tehran's UWS, based on the concept of “sustainable urban development” as a new viewpoint in urban development. A systematic analysis of sustainability of the system with a series of quantitative and qualitative criteria and corresponding indices thereof is necessary to assess sustainability level of Tehran's UWS as a whole and as distinct basins. A basic definition of sustainable urban water system is proposed, which is used along with index study in sustainable development and expert-suggested criteria to establish a set of sustainability assessment criteria. A combination of analytic hierarchy processes and Likert scale is, then, used to analyse the data collected through matrices and questionnaires. A series of indices are used to increase compatibility of the matrices or to control accuracy of experts' opinion. The analysis shows the absolute hierarchical weight of Tehran's UWS to be 0.592 (of 1), i.e. Tehran's UWS is in semi-sustainable state.