This dissertation assesses the long-term technological and policy implications of adapting to water constraints and climate change impacts in the energy sector. Energy systems are increasingly vulnerable to climate change and water resource variability. Yet, the majority of long-term energy infrastructure plans ignore adaptation strategy. New analytical approaches are needed to address the spatial and temporal scales relevant to both climate change and water resources. The research in this dissertation overcomes these challenges with improved engineering-economic modeling. Specifically, the conventional systems-engineering energy technology planning framework is extended to incorporate:​ (1) robust capacity decisions in the electricity sector in light of impacts from hydro-climatic change and uncertain environmental performance of technology options;​ (2) an endogenous, spatially-distributed representation of water systems and feedbacks with energy demand;​ and (3) multi-objective decision-making. The computational modeling framework is applied to four regional case study analyses to quantify previously unaccounted for policy-relevant interactions between water, energy and climate systems. Application of the robust adaptation planning framework to the power system in British Columbia, Canada, reveals technology configurations offering long-term operational flexibility will be needed to ensure reliability under projected climate change impacts to provincial hydropower resources and electricity demand. The imposed flexibility requirements affect the suitability of technology options, and increases the cost of long-term electricity system operation. The case study analysis then focuses on the interaction between groundwater conservation and concurrent policy aimed at reducing electricity sector carbon emissions in the water-stressed country of Saudi Arabia. Application of the novel water-energy infrastructure planning framework reveals that transitioning away from non-renewable groundwater use by the year 2050 could increase national electricity demand by more than 40 % relative to 2010 conditions, and require investments similar to strategies aimed at transitioning away from fossil fuels in the electricity sector. The research in this dissertation demonstrates the crucial need for regional planners to account for adaptation to climate change and water resource constraints when developing long-term energy strategy.