I wonder if a lot of the 19C denying about polluted water was from doctors taking umbrage at non-doctors pointing out what was really happening?
That happened with the link between mosquitoes and malaria, made when early efforts to construct the Panama Canal though swamps had such a high death-toll from the fever.
Similarly with “caisson disease” first reported among the builders of New York’s Brooklyn Bridge.
The doctors’ dogma about malaria, and I think cholera, etc., was based on an early notion about “foul miasmas” being the cause.