This is not a reasonable commentary on the law. The obvious rejoinder to your point is that the paper is printed once, and the glasses are filled many times a d

This is not a reasonable commentary on the law. The obvious rejoinder to your point is that the paper is printed once, and the glasses are filled many times a day. Another plausible rationale is that by creating a rule that applies to people's everyday lives in a visible way, the public becomes more aware of water savings in every context. Another plausible rationale is that politicians want to signal concern over water shortages to their concerned constituents, but for a variety of (probably well-intentioned) reasons don't want to change actually impactful regulations about water distribution, so they make a symbolic one. Like you, I assume that these are stupid reasons which don't warrant making the law. But pretending that they don't exist is not a good way to think. Argue against something real.