California, and specifically, southern california is made up of mostly arid and semi-arid regions.
The water has to be delivered, and has been, in the past, through monumental engineering, and visionary ways.
The population has doubled in the last forty years, yet we still rely largely, on a 70 year old aquaduct system.
Anyone who has lived here for any length of time and is somewhat educated (or just pays attention) on the climate patterns, understands that we have a pattern of "droughts", followed by short bursts of precipitation.
Desalination is the obvious answer.
Either that, or half of those people who moved out here need to go back to where they came from.