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)
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...
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.