Desalination is not there yet. A new age will come when the cost of desalinated seawater low enough for agriculture. Since many of the world’s deserts are next to oceans the size of habitable earth will expand substantially.
Oh yes, it is...see my above post about Aruba...
Have a look at Israel’s desal plants. They are producing 154,540,650,630 gallons a year.
There are low cost graphene/nanotube filters available which swap right out with traditional high cost filters — the format is the same. And the last I heard, the Koreans are working on bringing the production of graphene/nanotube desal filters way, way down through 3D printing.
Desal is here. Political will is not.