Water distribution networks are critical for the recovery of an urban area struck by a moderate to strong earthquake. In the paper a refined computational procedure is presented able to assess the post-seismic re-sponse of a water distribution system. The procedure permits to deal either a scenario analysis (when the earthquake that is going to hit the urban area is known in its essential features) or a full probabilistic analy-sis. In the latter case in input it is required to specify the basic parameters able to describe the seismotectonic framework around the area of interest. Other sources of uncertainty are due to network geometry and me-chanical response to seismic action. The reliability computation is based on the Monte Carlo method: each simulation caries out the generation of an earthquake (location and magnitude), the propagation of seismic effect at network nodes, the simulation of possible leaks and breaks over the pipes and finally the flow anal-ysis on the damaged network. The method is applied and discussed using a real case network.