So whenever you hear of a place running out of water, look at how many people live there. Those people will either die or leave, and before they do either, they will probably get into pretty bad fights over the dwindling water supply. Outsiders will likely give zero fucks ... until the leaving starts. They really don't want that to happen. They don't want foreigners trying to move in and live on their land and drink their water.
People should think ahead. If you don't want to be overrun by millions of refugees, take steps to protect the global water supply while there is still enough of it for people to stay where they are.