Israel uses 1016 million m^3 of water [1] or about 800,000 acre feet on agriculture per year. While studies have shown that California as a whole could save 5.6-6.6 million acre feet per year while maintaining productivity and the same acreage farmed [2]. It is a bit more difficult to restrict the number to the central valley, but the central valley accounts for more than half of California's total agriculture [3], so we can just use the statewide number.
The entire state's annual agricultural water usage is less than 45 million acre feet [2]. Even if Israel had all of this water they would max out at under 60 years.
1. https://en.wikipedia.org/wiki/Water_supply_and_sanitation_in... 2. http://www.nrdc.org/water/files/ca-water-supply-solutions-ag..., p.2 3. http://www.nass.usda.gov/Statistics_by_State/California/Publ... p.22-38