Not good at all. This is what happens when a major population lives in an arid area. It's just a matter of time before a weather anomaly comes along and causes havoc. We've had similar issues on the west coast of Oz, but admittedly we get 3 times So Cal's rainfall and we have around 2 million population so we are nowhere near as efficient in water use as those in So Cal. Here they have built desalination plants along the coast. These use large amounts of energy, but we are now seeing more and more wind farms being set up to supposedly take the pressure off fossil fuel energy production.
I don't envy So Cal's situation. Often governments, instead of being forward thinkers and planning for these inevitable situations, just hope it doesn't happen in their term of office and do nothing or very little, until the problem is so severe that doing nothing will cost them votes. Here in the west of Oz, we have a huge water source in our tropical north, that dwarfs all water sources around, in Lake Argyle in the Ord river. They've been talking about bringing a pipe down to Perth since the 60's. It seems they can do it with a gas pipeline, but as yet they've done nothing with the water pipeline. I suppose you can't export water.
I think water will be one of those most valuable resources that as Earths population climbs and we keep damaging the environment will likely be the cause of future conflicts and problems.