Sun sets on a Merced County, Calif., farm as water is conveyed in an unlined canal to more distant fields.
Sun sets on a Merced County, Calif., farm as water is conveyed in an unlined canal to more distant fields.

California's water-rights regulators have allowed five times more surface water than the state actually has, making it difficult for them to tell whose supplies should be cut during a drought.

University of California researchers analyzed the state's water-rights allocations to come to that conclusion.

As a result, they say that the State Water Resources Control Board, which regulates water rights, needs to systematically overhaul its policies and procedures to bridge the disparity gap. Unfortunately, they say, the board lacks the legislative authority and funding to do so, according to a news release.

Ted Grantham, who examined the state's water-rights database as a post-doctoral researcher with the UC Davis Center for Watershed Sciences, said the time is ripe to improve the water accounting system.

"Given the public's current attention on drought and California water, we now have an unprecedented opportunity for strengthening the water-rights system," Grantham said in the release.

Better information also might be able to help state regulators target water cutbacks during droughts.

The state has allocated a total maximum allowable use of 370 million acre-feet of water. That's more than five times the 70 million acre-feet available in a year with good precipitation, according to the researchers' review of active water rights.

The researchers blame the complicated and backlogged system for the mismatched accounting.

Some users, for example, take water and then apply retroactively for the water right while continuing to take it. This may occur for up to a decade while their application is pending.

Inaccurate reporting—whether deliberate or accidental—by water-rights holders only worsens the problem.

The result is that in most water basins and during most years, far more people hold water rights than there is water.

In the San Joaquin River basin, for example, water-rights allocations exceed the river's average annual fold by eightfold.

An acre-foot, about 326,000 gallons, meets the annual water needs of a family of four to five, according to the California Department of Water Resources.