Water and electricity systems are crucial lifeline infrastructure systems that support urban production and residential living. This paper proposes a reliability assessment method for coupled water-electricity systems under seismic actions, based on spatial seismic ground motion fields and seismic vulnerability models of system components. Seismic motion parameters are calculated at various spatial locations according to their attenuation relationships. Using Monte Carlo simulations, samples of seismic damage to system components are obtained to assess the connectivity reliability of the water-electricity system under scenarios of component failure, thereby determining the system’s seismic connectivity reliability. To consider the coupling impact of damage to the electricity system on the water supply system, the post-earthquake connectivity of electricity nodes supplying power to water treatment plants is analyzed to determine the operational status of water supply source points post-earthquake, further evaluating the connectivity reliability of the water supply system. Using a 29-node water system and an IEEE 30-node electricity system as examples, the reliability of various nodes and lines within the water-electricity system is assessed from different dimensions.