Climate change impacts on California’s environment are evident, especially when it comes to our water cycle. The state’s natural climatic volatility is increasingly marked by hotter and drier droughts and less frequent but more intense wet periods. These shifts not only stress California’s water supplies, they also affect energy supplies in important ways. For instance, less water in reservoirs increases drought vulnerability, and it also hinders hydropower production.

There’s also a relationship between water and energy on the demand side: the water system uses more energy than many realize for conveyance, pumping, and (especially) heating. This presents opportunities to save energy by saving water—helping to decarbonize the economy along the way. Our new fact sheetexamines the points where California’s water and energy systems overlap and identifies pathways for reducing risks and promoting smart conservation.

California’s water system is a big energy user

The water system is a major energy user in California: according to the most recent data available (from 2001), one-fifth of the state’s electricity and nearly one-third of its natural gas go to pumping, conveying, treating, heating, and other energy-intensive water uses for homes and businesses. Managing energy use in the water system will be important as California works to become carbon neutral by 2045.

Simply reducing water use—already a key drought resilience strategy—can help save energy. During the last drought, for example, water conservation led to substantial energy savings.

Heating water stands out as a very energy-intensive element of the water infrastructure, comprising fully one quarter of total residential energy use. Water heating, along with other energy-intensive water uses in homes and businesses, makes up almost 90% of water-related energy use—while treatment, pumping, and conveyance account for the rest. Reducing hot water use and improving water-heating efficiency could significantly decrease California’s overall energy consumption, and switching from gas to electric water heaters could help meet decarbonization goals.

Our energy sector also relies heavily on water

Water is a key component in generating energy—turning hydropower turbines, cooling thermoelectric plants, and aiding in oil and gas extraction. And this water dependence is rendering California’s energy sector increasingly vulnerable: thermoelectric plants that rely on surface water for cooling, for example, may face shortages during droughts.

The most vulnerable energy technology is hydropower, which makes up 15% of California’s electricity portfolio on average. Hydropower generation varies from 7% of California’s electricity in dry years to over 20% in wet years. As climate change pushes the wet and dry periods to extremes, hydropower generation may become even more volatile, threatening California’s energy reliability.