Despite what you might think water is not a particularly limited resource.

At the municipal level 1 cent ~= 1,000+ gallons of water but this can vary greatly by location. As a customer in many ways you are paying for pipes not water.

PS: California farmers often pay ~70$ on average per acre foot or 325,851 gallons. But, they also get a lot of water for far less than that it's the rare edge cases that are really expensive. http://westernfarmpress.com/water-70-24-million-acre-foot