But that's not the choice a market provides to people, nor would it be the choice for most people even without the current market framework for presenting choices.  Someone in Iowa, USA, where water is abundant, would be completely correct in his belief that if he never used that water, no one else in the world would be able to either -- it would flow, eventually into the Gulf of Mexico because no one who might need it where water is scarce could ever get it even if he bought the water for the price of a movie ticket and set it aside for that person.  Water in abundant regions is not closely enough connected to water in scarce regions to be able to make the comparison you do, so for many people, under any ethical considerations, a movie ticket can be worth more.