These kinds of questions should be ignored. It's a ridiculous nonsensical premise and even attempting to address it directly is a waste of time. There is some value in discussing why this is a stupid question, but none in trying to answer it. A village of 100 people has one well owned by one person. And he "suddenly" decides not to let anyone have water. No context there. There's no other source of water, at all, a situation which would never result in a village of that size, and everyone else is dying of thirst. Dying. So not only do we have an impossible situation, with no context, but we are asked to moralize about it at the last possible instant. And then the person posing the question says, "Don't say it can't happen," because he doesn't want you to be able to call him out on his bullshit.
I used to teach karate. Inevitably, a student would ask, "What do you do if a person is just about to hit you in the face. They've already thrown the punch, your hands are down, and their fist is an inch from your face." The answer is, "You get punched." In such a ridiculously contrived scenario, there is no answer. It's an impossible question designed to waste your time and discredit a moral theory. It could not happen, it would not happen, and it should not be discussed in the context of philosophy.