[SEMW]

Distribution based on need (means-testing) seems to scale poorly. You need a system to determine means, which at governmental scales is inevitably bureaucratic, resource-intensive, and prone to cheating.

Point is, it is always possible to take a means-tested system and turn it into a universal system without changing the final distribution.

Take your thirst example. Say nine people have 100 units of water and the tenth has 0. A means-tested welfare system might involve taking 5 units from each of the 9 people and giving it to the tenth, leaving the nine with 95 and the tenth with 45. Now, instead, we increase the 'tax' from 5% to 50%, and give everyone 45 units. The resultant distribution is the same (the nine have 95, the tenth has 45), but this way involves no means-testing.

OK, so the numbers here are a bit unrealistic, but the point is, given any means-tested system you can always make it universal and just make the tax system more progressive to cancel out the benefits paid to the non-needy.