california gov. jerry brown ordered state officials wednesday to impose mandatory water restrictions for the first time in history .
brown said he signed an executive order requiring measures be implemented to cut water usage by 25 percent compared with 2013 levels .
state water officials found no snow on the ground at the site for their manual survey of the snowpack .
snow supplies about a third of the state 's water .
a higher snowpack translates to more water in california reservoirs to meet demand in summer and fall .