Iran depends on desalination for around 3% of its drinking water, and has said that any such attacks on its infrastructure will see the same to any country that has support the USA/Israel military actions.
USA allies in the region will be largely uninhabitable, since they depend on power and desalination for their existence.
Still, maybe that is what Trump, the crazy bastard, wants.
Yeah, the amount of magical thinking about this conflict in the USA is disturbing. Iran is dry, but it's not just desert. The military will have backup generators and priority access to any generator infrastructure or repair capability. The ones that will suffer are the civilians, and the fanatics will just see that as martyrdom.
You can't defeat religious fanatics that welcome pain just by inflicting pain, especially by inflicting it mainly on other people.