Making rainwater harvesting illegal (and thus forcing people to overpay a monopolized water system) is arguably a violation of human rights. It is a prohibition of what you are 'free to do for yourself', that forces people to pay for something they need to survive (and could otherwise get for free).

However, I agree on the haziness around the issue. Mandating that everyone receives X amount of drinkable water may be expensive to implement, economically unsustainable and create perverse incentives.