They only have two long-term options:

1) depopulate those regions by causing folks to leave (e.g. no longer providing water services)

or

2) deploy costly (and energy-intensive) mechanisms to continue to provide water (desalination, or piping in water from some other place that will likely dry up next)

Desalination has high capital costs, but the energy usage isn't really a problem at all.

A modern plant uses 2.5-3.5 kWh/m^3 [1]. My household uses something like 9 m^3 per month, so that would be about 27 kWh per month. At PG&E's rather high peak rates, that's $10/month, which is less than the marginal cost of that water. Of course, to the extent that energy costs matter, desalination plants will not use retail power at peak times.

[1] https://www.amtaorg.com/wp-content/uploads/7_MembraneDesalin...

are there any consumer desalination units available that one can buy and setup in their home?

But where do you get the salt water?

So Cal can deff run off desal plants. Esp L.A. and San diego. Phoenix and Vegas might not be a place you want to invest in real estate.

Arizona actually has a lot of brackish and brine well water that is non-potable.

A lot of it is actually in the Gila Bend area, where people have been trying for decades to figure out something to do with it - there used to be a company that grew "desert shrimp" in ponds using the water. Later, during the housing crisis (for some reason) they tried to make a go of growing algae (in cooperation with one of our universities - maybe ASU) in the ponds by piping CO from diesel aeration pumps into the ponds - then harvesting the algae (which were high in lipids) to make biofuel.

Ultimately, I don't think either of these panned out, but the water is there.

Thats very optimistic. The gila river is tiny compared to the population of Phoenix. Unless there's more water somewhere I'm missing.