Were the youths correct in withholding water from the intoxicated non-Muslim, and are there any religious texts to that effect?

The man should have been given water with the intention of reward, for in every wet liver there is a reward. Then he should be invited to Islam, if he is not Muslim, by explaining its virtues. If he is Muslim, he should be called to adhere to the law of Allah, and it should be clarified to him that this forbidden act is not befitting a Muslim.