Ya know, you're assuming all water used in ag is pumped out of the ground. True in some areas, not in others. And that it's not replenished fast enough -- true in some areas, not in others.
I find it rather telling that the most resistance to building dams to store the winter melt comes from areas with the most hue and cry against ag water use. (Did you know that some parts of the Sierra Nevada can achieve a snowpack in excess of 50 FEET?? Where do you think all the water goes in the spring?)
There are parts of Calif that are now desert, but were not before Los Angeles siphoned off all the surface water. Think on that.