Desalination is not trivial. It must be done on the coast and produces truly immense amounts of brine which kills everything, -- all plants, all animals -- in the vicinity. People talk about desal as if you can just plop a plant anywhere and get infinite water, but it does not work that way, you need to manage the brine. Either you commit ecological genocide or you find a way to pump corrosive salt water miles out to sea (and in a spread out network of underwater viaducts to keep the concentration down). Very very expensive.

It's basically a non-starter at agricultural scale. It's suitable only for small amounts of drinking water.