If the water season improves, it could increase the allocation, according to a news release.
"We hope things improve with this winter's storms," director Mark Cowin said in the release. "But there is no guarantee that 2014 won't be our third consecutive dry year."
The department operates the State Water Project, which delivers water to 29 different public agencies.
On average, about half of the state's precipitation occurs from December through February, with three-quarters occurring from November through March.
The initial forecast is called conservative because it's made before the wettest part of the year. The 2013 forecast is the same initially made for 2010 coming off the 2007-09 drought.
But unusually high winter precipitation prompted water resource managers to increase the allocation to 50 percent for 2010.
Storage levels at the state's major reservoirs also factor into the initial allocation.
Lake Oroville in Northern California, the State Water Project's principal water storage facility, was at only 41 percent of capacity Nov. 20.
Historically, the reservoir would be at 66 percent on this date.
Lake Shasta, the federal Central Valley Project's largest reservoir, stood at 37 percent capacity. And San Luis Reservoir was at only 25 percent capacity.
For the 2012 season, the State Water Project allocated 35 percent of the 4.17 million acre-feet requested by agencies. An acre-foot of water—enough to cover a football field with 1 foot—can meet the annual water needs of an average family of five.
The last time the project delivered 100 percent of requests was 2006.