How sterile are water reservoirs and lakes? My guess is they're full of pooping and dying fish, bugs, god knows what. The big city nearby me pump drinking wat

How sterile are water reservoirs and lakes? My guess is they're full of pooping and dying fish, bugs, god knows what. The big city nearby me pump drinking water out of the same lake they pump treated and untreated sewage into. The suburb I live in at least uses well water. My point is if the source of the water is full of living and dead animals and bugs then worrying about homeless people peeing on the fountain remains gross but is no longer a serious concern. Pumping that same water into a bottle and charging a large amount of money for it doesn't make the problem go away either.