It appears the solution to most hard or intractable problems is to post pithy aphorisms on the internet.

As far I remember a large reason for the water crisis is subsidizing water for agriculture which does not fit the local climate

This is based on some ideological pillar of being autarkic, as the Islamic Republic was generally built upon the fear of outside influence

sounds like if 90% of their water goes to agriculture, mostly export, and their country is cash strapped due to their habit of kidnappings, then maybe there's a simple solution here

I like the idea of working with nature to solve problems. As a start, instead of, as you suggest, depopulating Tehran, they could populate it with trees. Chad is a perfect example of how to turn a deserted landscape into a "Great green wall of Africa" as they call it. And they did in only two years.

Use less water? Probably by recycling the water that is actually used. If las Vegas can survive in the desert, any city can. The problem is getting the money to apply the fixes required.