You don’t even seem to have a basic understanding of how city water supplies work. No amount of people shitting in the woods makes your drinking water contaminated; where the fuck do you think animals shit?

Edit: there are absolutely public health concerns to be made about human shit being around where people do things, especially non porous surfaces which don’t offer opportunities for decomposition. But that’s a problem to be solved with better public restroom coverage, even housed people will pee/shit in public when there isn’t a restroom available