Large-scale assessments of the vulnerability of electric infrastructure are usually performed for a baseline water year or a specific period of drought. This approach does not provide insights into the full distribution of stress on the grid across the diversity of historic climate events. In this paper we estimate the Western US grid stress distribution as a function of inter-annual variability in regional water availability. We softly couple an integrated water model (climate, hydrology, routing, water resources management, and socioeconomic water demand models) into an electricity production cost model and simulate electricity generation and delivery of power for combinations of 30 years of historical water availability data. Results indicate a clear correlation between grid vulnerability (unmet electricity services) for the month of August, and annual water availability. There is a 21% chance of insufficient generation (system threshold) and a 3% chance that at least 6% of the electricity demand cannot be met in August. Better knowledge of the probability distribution of the risk exposure of the electricity system due to water constraints could improve power system planning. Deeper understanding of the impacts of regional variability in water availability on the reliability of the grid could help develop tradeoff strategies.