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.

Remind me, who controls the House, the Senate, and the Presidency in the US? And how do you propose building all of this infrastructure? Are we going to put peoples' taxes to work on this kind of problem? What makes that a more valid use of the money versus water conservation efforts? Is it just that this is your dream, much like Germany once dreamed of farming the Mediterranean sea floor?

What is your plan for dealing with the super-brine which is also produced by desalinization?

You might want to check a topographic map of Mexico and exactly where Mexico City is located before being so dismissive. It's in an elevated plain (more than 2km elevation), surrounded by mountains in the middle of the country, ~300km from the closest sea. Also, it's a seismically active place, with active volcanoes, and with highly unstable ground that is sinking.

While desalination is unquestionably a good solution to combat the overconsmption of water in many places, aqueducts from desaliatnion plants on the sea coast to Mexico City would be extremely expensive. And you'll have to figure out what to do with the salt brine.

Mexico City is 7,350 feet above sea level.

I'm still waiting for the Solarpunk future I was promised as a child.

Which flower children are in power at this time?

...of our own creation.