California’s water system uses energy to pump, convey, treat, and heat water. Although agriculture uses roughly four times more water than cities, cities account for most water-related energy use. Water is also required for hydropower generation, thermoelectric power plants, and oil and gas extraction. Improving water use efficiency can reduce energy consumption; conversely, improving energy efficiency can reduce impacts on water supply and quality. … The water system uses approximately 20% of the state’s electricity and 30% of its natural gas for business and home use, according to data from 2001—accounting for more than 5% of California’s greenhouse gas emissions.