The problem is that many don't understand what the word "infrastructure" means. It's all that unsexy stuff like roads, reservoirs, dams, power transmission systems and pipelines (water, oil and gas).

Yeah. Republicans don't understand that word, and so ignore it until it fails.

A better source than Xhitter: BBC: Iran faces unprecedented drought as water crisis hits Tehran

I don't think infrastructure is the main problem. They have dams, and had reservoirs. But they don't have much rain, so the reservoirs aren't being filled. We're seeing the same thing in the American Southwest, where lakes Powell and Mead are both near record lows (since they originally filled decades ago). The problem here is inefficient agriculture (i.e. growing water-intensive crops), and too many people sucking too much water in an area (i.e. desert) that isn't really suited to supporting that kind of population (i.e. not much rain). I don't claim to be an expert on Iranian infrastructure. However, I suspect their main problem is similar to ours (i.e. drought). If you don't have groundwater wells, and you don't have rain, then you don't have water.

At least Iran has a sea nearby. They could build desalination plants. Arizona really can't.

It will be interesting (and remarkable) if they actually evacuate Tehran. I doubt that will happen. But a large migration of a significant chunk of the population may happen organically as people seek someplace where they can survive.