[Kliment]

Basically, it's super-expensive to check actual need, and by removing the administrative expense related to it you end up getting a much more efficient system. There's also the side effects of making part-time employment easier and speculative/entrepreneurial projects safer. To match your analogy, if it costs 11 units of water to determine who is thirsty, then giving water to all ten costs 10 units, and giving water to just the one costs 12.