John Snow and the Broad Street Pump
Again, on that same 'public health visit' I walked past the replica Broad Street pump from which Dr John Snow famously removed the handle in order to halt a cholera outbreak which, he had determined, came from the pump water due to the first use of epidemiological mapping.
The pump has been relocated since I last went to visit it - it is now directly in front of the John Snow public house (on the right in this photo) - named in the good Doctor's honour but ironical as he was teetotal (in addition to being an anaesthetist for Queen Victoria's later child-births).
This all happened in 1854 ($5,220 GDP per person at 2020 PPP values), equivalent to an Upper Middle-Income country in today's understanding.
But it was the Reverend Henry Whitehead who, in an attempt to disprove Dr Snow’s hypothesis, found the cesspit that had contaminated the well ….. there are no plaques for finding faulty pit latrines!