"Rules of war" don't really work the way people think they do.
The reason why armies follow what appear to be "rules" is very simply because not following them is counterproductive to their goals.
Governments are nothing without an air of legitimacy, so the hearts-and-minds battle is positively central to any campaign.
It's quite plausible that the reason why Iran has not hit the Israeli desalination plant is because there are enough Muslim Palestinians who would die if Israel ran out of water, that it would harm Iran's standing with the wider Muslim community. It has nothing to do with Geneva Convention saying that civilian infrastructure is a no-no.
But this doesn't mean that they can't cluster-bomb Tel Aviv. That's also a "war crime", but it's not one that they really have to care about. Same goes for Israel using white phosphorus in Lebanon, it's a war crime, but not one that they really have to care about.
Russia was VERY gentlemanly in the early days of the Ukraine war, and this was because the international community was watching them, and public support for helping Ukraine was conditioned a lot on public perception of Russia as a terror state. But 4 years later nobody is watching anymore, so they now feel that destroying Ukranian power and heating infrastructure is not going to have any real down-sides for them.
