The civilian price will be terrible. But this could be one way: Destroy all power plants and desalination plants. Rations will be given out by “peace keepers” on the condition that IRGC members surrender and are taken prisoner. Missiles and drones can be exchanged for rations as well.
Hitting desalination plant will mostly (and almost only) hurt the population outside of IRGC power circle, exactly the population the USA incited to rebel for a few years, with pakistani help. Basically South Alborz. Iran did have a water crisis, but it was agricultural water that made them have to import more food, not an issue of drinking water. The only way to truly start a global Iranian famine (what a terrible weapon tbh, i can't help but to think less of people who think about using it, it's impossible for me to stay neutral,it is an inhumane stance, and i would be ashamed of having it) is to block Iran northern trading routes to Russia/Kazakhstan/Azerbaijan, which, to be clear, is impossible.
Ah yes the true and tried strategy of civilian bombing, worked so well for: the nazis bombing campaign against the UK.
Same goes with Russia against Ukraine.
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.