When the water is $1-2, I have no problem with buying several throughout the night, but when its $4 I'll resort to sticking my face under the sink before I'll pay those kinds of prices.
I know for a fact that those things run less than a dollar when you buy by the case, that kind of markup on a product that could mean the difference between a good time and a trip to the hospital (for certain people) is just irresponsible IMO.