Seismic serviceability of a water supply network refers to its capacity to meet the particular water demand（flow and pressure） in a city after an earthquake.After an earthquake

the water supply network is usually under varied pressure deficient conditions leading to a shortage of water supply at some nodes of the network so that some of the network users cannot be fully satisfied on water pressure and water flow.Therefore

a set of nonlinear hydraulic equations were formulated

considering the dynamic variation of nodal flows with nodal pressures on the basis of the conventional hydraulic analysis of the network

to solve for real flows and pressures at nodes of the network.At the same time

the analysis method of structural reliability was borrowed to introduce the first-order-second-moment method and a probabilistic hydraulic model for the serviceability analysis of the network.A real network was taken for an example to demonstrate how to apply the serviceability analysis of water supply networks based on varied pressure deficient conditions after an earthquake.