Also, the water that those people would actually manage to scoop up probably wouldn’t keep them alive for long. Unless those splashes into the crowd were frequent, but it seemed like a semi-rare treat. So it doesn’t make any sense, no matter how you look at it.
The dissonance of resources like water and fuel being scarce, and at the same time being wasted frivolously, runs through the movie. See: Flame-throwing guitar. Also, the scene where the wives are cleaning themselves off, where they don’t seem to be particularly concerned about conserving water.
Doesn’t matter: The logic that this movie runs on isn’t strictly logical logic. It’s thematic logic. (If that’s even a term. If not, then, hey, it is now. ;))