Brown issued the executive order from the Sierra Wednesday in an area that would once had a snow pack measuring 5-feet deep at this time of year.
Standing on brown grass in the Sierra, the Brown delivered a grim report on California's drought.
"We're in a historic drought and that demands unprecedented action," Brown said.
The mandatory water restrictions call on water agencies to start charging more for excessive water use, require new homes to have water-efficient drip irrigation and require golf courses, cemeteries and other large spaces to use less water.
All that because the snowpack, which accounts for about 30 percent of the state's water supply, has dipped to 19 percent of normal for the date, the lowest on record.
If Californians don't cut their water usage by 25 percent, it means water districts would begin charging extra.
"If it comes to, if the regulations mandate that, that's what we'll do. We'll basically set a water budget for every house and the chips will fall where they may," said Steven Ritchie of the San Francisco Public Utilities Commission.
"So the 25 percent will be measured against water use back in 2013 before the drought began," said Mark Cowin of the state Department of Water Resources.
"I could make the washer go into a grey water system, I have not done that," said Rita Roti, a San Francisco resident.
VIDEO: Benicia begins tight water restrictions for spring, summer
Last year, San Franciscans reduced their water use by eight to nine percent, systemwide 14 percent.
The 2.6 million customers in the Bay Area who rely on Hetch Hetchy for their drinking water supply haven't done enough.
"I'm meeting with them tomorrow, our wholesale clients to put everyone on notice that it's belt tightening again," Brown said.
Those include wholesalers in counties like San Mateo, Northern Santa Clara and Southern Alameda.
VIDEO: Bay Area businesses targeted by new water mandates react to restrictions
For water rebate information from Bay Area water suppliers, click here. And click here for tips on how to conserve.
For full coverage on the drought, click here.