[dragonwriter]

California has very roughly a billion acre-feet of groundwater capacity[0], and it is so severely depleted from being pumped out to cope with surface-water shortfalls over the years that the Central Valley is sinking (and eroding groundwater capacity in the process.)

California doesn't need 75 million more acre-feet of surface water, but it could probably benefit from multiples of that being pumped back into the ground.

[0] CA Dept of Water Resources estimates between 850 million and 1.3 billion, http://waterinthewest.stanford.edu/groundwater/recharge/