Paying for water is rationing water--think of your dollar bills as rationing coupons.
What's next, air?
There are surely certain public interests in rivers, lakes, reservoirs, etc., but why should there not be a market for water as there is for virtually every other resource?
Air is not comparable. It's virtually infinite, uniform, and totally mobile. Water abundance varies by location, and is very expensive to store or transport. The people and infrastructure required to store and transport it need to be paid for. Therefore water costs money.