Water and energy are inextricably linked in California and, as one resource faces constraints or challenges, so does the other. With the state looking to both reach its climate change goals and decarbonize its economy through a transition to 100 percent clean energy, water will play an integral role. Water is a key input for energy production, and energy is integral to all aspects of water management and use in California—including collection, treatment, heating, and wastewater management. Prior studies have estimated that about 20 percent of California’s total statewide electricity use, a third of non-power plant natural gas consumption, and 88 billion gallons of diesel consumption are related to water—from collection and treatment to use and wastewater management—with a large share associated with heating water. These interdependencies between water and energy supplies are commonly referred to as the water-energy nexus.