The whole point of the 'naming the Broad Street Pump' is that it was identified as the source of a cholera epidemic that was sweeping that part of London at the time. Snow had the bright idea of charting where the cases were and investigating the area. It turned out that all the victims had drawn their water from that particular street pump (no water piped into houses then, it was gathered at a street pump or well, and bucketed home) and that was the source of the infection. He had the pump disabled and the cases of cholera stopped almost overnight.

Thus was born the ideas of water borne infections and forensic medicine.

LTS