The California Department of Water Resources, which operates the State Water Project, has decreased the amount of water it plans to deliver to 50 percent of the requested amount.
Deliveries will amount to slightly more than 4 million acre-feet, according to a news release.
State Water Project managers blamed the "stubbornly dry conditions this winter" for the delivery reductions.
Originally, the department had projected 60 percent deliveries.
The state water year runs from Oct. 1 through Sept. 30.
Runoff in both the Sacramento River and San Joaquin River systems is projected to be far below average.
In the Sacramento River basin, for example, state water managers predict a Feb. 1 median runoff of 9.4 million acre-feet, the 16th dries in 106 years, according to the release.
In the San Joaquin River basin, the Feb. 1 media runoff is predicted to be 3.2 million acre-feet, the 21st driest in 111 years.
Much of the state's runoff comes in the form of snow that falls in the Sierra Nevada and feeds into the Lake Shasta basin to the north and the American River basin to the south.
Eight precipitation recording stations in the area show only 51 percent of seasonal precipitation average.
A five-station index in the San Joaquin River Basin shows only 47 percent of seasonal average precipitation.