By Jeffrey Mount and Emma Freeman.

The ongoing drought has heightened tension over how water is allocated in California. In our recent publication on overall water use in California, we show that the environment uses the largest share—50%—of the state’s water. In contrast, agriculture uses 40% and urban users account for only 10%.

The amount going to the environment may look surprisingly high, but this number is not as straightforward as it may seem. Most of what we call “environmental” water is simply too remote for people to use—or is actually reused for irrigation, drinking water, or other human benefits. In other words, most of the water that goes to the environment does not significantly detract from the overall amount of water available for other purposes.

Here, we look more closely at how the California Department of Water Resources breaks down environmental water use (also see related figure below):

    • Managed wetlands make up state and federal wildlife refuges and account for only 4% of total environmental water use. These wetlands provide critical habitat for migratory and resident birds, along with fish, plants, and other wildlife. Some provide other important ecosystem services like flood protection.
    • Delta outflow accounts for 16% of total environmental water use. The state sets standards for how much water should flow into the Delta from the Sacramento and San Joaquin Rivers, and how much should flow out of it, into San Francisco Bay. These standards seek to meet two primary objectives: protection of native fishes listed under state and federal Endangered Species Acts, and maintenance of water quality standards within the Delta—most notably for salinity—to allow irrigation of farms in the Delta and exports of water to cities and farms elsewhere.
    • Instream flows constitute 18% of statewide environmental use. These are minimum river levels set by state regulatory agencies to meet habitat needs for fish and wildlife in waterways.
  • Rivers designated as “Wild and Scenic” use the bulk of water assigned to the environment—63%. Under federal and state laws, these rivers are protected from the construction of water resources projects—such as dams or diversions—that would adversely impact them. However, most of these rivers are in the state’s remote north coast, where there is little agricultural or urban demand for water and no economically viable way to use it elsewhere. Outside of the north coast, most water in Wild and Scenic Rivers (such as those on the west slope of the Sierra Nevada) is captured in downstream reservoirs and used again for hydropower generation, irrigation, and drinking water.

As this discussion shows, the allocation of limited water supplies is not a matter of simple tradeoffs between the environment and humans. Sometimes, water counted toward environmental use gets used again for something else. Other times, there is no practical alternative use (such as in the north coast). Understanding these basic facts is essential to resolving differences over how to manage water in California.

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Originally posted at the Public Policy Institute of California.