The　serviceability　of　water　supply　networks　(WSNs)　under　seismic　loads　has　significant　importance　for　estimating　the　probable　losses　and　the　impact　of　diminished　functionality　on　affected　communities.　The　innovation　presented　in　this　paper　is　suggesting　a　new　strategy　to　evaluate　the　seismic　serviceability　of　WSNs,　utilizing　their　operational　physical　mechanism.　On　one　hand,　this　method　can　obtain　the　seismic　serviceability　of　each　node　as　well　as　entire　WSNs.　On　the　other　hand,　this　method　can　dynamically　reflect　the　propagation　of　randomness　from　ground　motions　to　WSNs.　First,　a　finite　element　model　is　established　to　capture　the　seismic　response　of　buried　pipe　networks,　and　a　leakage　model　is　suggested　to　obtain　the　leakage　area　of　WSNs.　Second,　the　transient　flow　analysis　of　WSNs　with　or　without　leakage　is　derived　to　obtain　dynamic　water　flow　and　pressure.　Third,　the　seismic　serviceability　of　WSNs　is　analyzed　based　on　the　probability　density　evolution　method　(PDEM).　Finally,　the　seismic　serviceability　of　a　real　WSN　in　Mianzhu　city　is　assessed　to　illustrate　the　method.　The　case　study　shows　that　randomness　from　the　ground　motions　can　obviously　affect　the　leakage　state　and　the　probability　density　of　the　nodal　head　during　earthquakes.