The level of service provided by municipal water system (MWS) is one of the key issues facing the water industry today. The hydraulic reliability of a MWS can be defined as the probability that the system can provide the demanded flowrate at the required pressure head. In this paper, reliability is expressed by nod reliability, estimated through extended-period simulation using nod-head analysis that predicts the availability of pressure at different nodes during deficient conditions. Due to the random nature of four water demand patterns and required pressure head, the prediction of water distribution system reliability for the future is subject to uncertainty. For purposes of application, a real municipal water system consisting of 24 pipes and 16 demand nodes is used. This applied approach can be used in the analysis or upgrading of existing systems, or the design of new systems.