Those areas, by force. Open a history book and stop trying to make political points with ridiculous hyperbole and flat out lies. People are not receptive to bad news when you intentionally and artificially make the news 10x worse by lying. Water usage is a serious problem. Yes. And there will still be a tomorrow.
Desalination does not require fossil fuels. It requires energy. Of which there are many forms. Some of those forms are renewable. It’s not an emergency measure. Desalination happens regularly, right now, today. Read a book.
We could desalinate ocean water with renewable energy. But that doesn’t help the idiots who think they are entitled to live in Arizona / the desert.
People can move.