It is public health and a smart idea for municipalities to provide it, but that doesn't make it a right (I'm not saying you're implying that btw, just continuing the debate.) If it was a right, every incorporated village, town, hamlet, etc... would need to provide it instead of making rural homeowners put in a septic system and dig a well, or at the very least foot the bill for those two things in areas it can't be provided.
That's not how it is though. Cities run water and sewer lines, charge a connection fee for homeowners who would like the service then the homeowner is responsible for paying some of the cost. A few rural areas where the lines aren't run may end up subsidizing the cost for a service they can't utilize, but it's a lot closer to a better system then providing a government luxury that is specifically designed around how much you make.