Earlier quoted context omitted.
This seems to be a common fallacy: desal, which is being considered by a few wealthy urban water districts on the coast, will do absolutely nothing to alleviate overpumping by farmers in the Central Valley.
I think the goal would be to scale desalination efforts to the point where it can replace groundwater pumping statewide. This would come at a huge cost, sure, but once the groundwater runs out, the economics won't look so bad.
The largest desal plant I am aware of is in Saudi Arabia and produces about 830 acre-feet of water a day. Irrigation Central Valley averages 110,000 acre-feet a day, although there are significant seasonal differences. Let's (generously) pretend that you somehow had space in coastal California (not exactly something we have a lot of here, and certainly not cheaply) to build ~60 desalination plants, each double the size of the largest plant in existence. Let's completely ignore the multiple gigawatts of additional power you'd need to run these things. Let's pretend that you somehow convinced the Coastal Commission, EPA, DFG, Fish and Wildlife Service, and all the other relevant entities that intake and discharge from several dozen huge new desal plants dotting the coastline would not significantly impact the marine environment. (Ha.) Assuming all that were true, you would still need to pump roughly 40 million acre feet of water a year from the coast, towards the foothills, in the complete opposite direction which nature intended.
Never. Going. To. Happen.
Sorry to rain on your parade, but this blind, frequently uninformed faith that Technology will save us from anything and everything just gets annoying after a while.