I'm beginning to hate religious people.

[Ace Otana]

But, given the scenario I presented to be true, the friend who would want to share the water would be doing a good thing, wouldn't he?

It is nothing but a belief, you could be wrong.
You see, as an atheist. I'm standing on the outside looking into your beliefs and viewpoint, and carefully judging and examining it. Seeing if it has any truth to it or not. Looking for ways to verify your claims before passing judgement. Not only are you christians telling us that you're the right ones and it's your god and beliefs that are true, muslims and other faiths are saying the exact same thing.
I've withheld judgement until I can verify/confirm one claim over another. So whether you think it's a good thing or not, I'm in the interest of what's true and real. I want to see reality for what it really is, and if reality is a world without a god and afterlife then I'll accept that as reality. I go where the evidence points. I don't just take people's word for it.

Anyway, here's my counter scenario: The theist finds a well and drinks from it without hesitation, he's now refreshed. He finds the thirsty atheist and tells him of the well. The atheist quickly tastes the water to see if it's ok but notices that it has high concentration of lead in it and that it has a few unknown chemicals in it. The theist dies 30 mins later and the atheist finds a road that leads to civilisation.