There is absolutely zero reason that California's cities cannot be fed with nuclear heated desalinated seawater or heck, traditionally desalinated sea water.
The only thing holding back this engineering solution are NIMBYs, naive greenies, and mountains of legal paperwork.
Water doesn't go away and we have the solutions to make freshwater. The problems are political, not technical.
Tha solves the city consumption problem which can then allow water run off from the mountains back into the valley where it used to be. That will help restore the aquafiers.
Read up on what the California valleys used to look like before the water was siphoned away to the coastal cities.
Edit: the replies and downd00ts to this post are precisely why California is in its current state. All whiners and no solutions. Enjoy your mess and desertification!