California

... and landscaping uses as well.

Furthermore, it's complete madness to burn fossil fuels to desalinate seawater since global warming will only make droughts worse.

Desalinization is not too expensive for indoor domestic use. It's usually advertised as a "half cent a gallon," which is less than it costs to heat water for a shower, but magnitudes greater than farmers pay for water.

Most people can afford to pay a penny to flush a toilet. If major dairy operations had to use desalinated water the price of milk would skyrocket.

The environmental impacts of desalinization go beyond dumping the salt. Various chemicals used to keep desalinization systems from fouling also end up in the waste stream as well.

I don't think any urban areas are going to dry up and blow away because of drought. Phoenix and Las Vegas are safe, they'll probably buy water rights from California, and California cities will in turn recycle sewage and desalinate sea water.

But agriculture in the Western U.S.A. is going to become a less viable business.