Background
"In the mid-19th century, the Soho district of London had a serious problem with filth due to the large influx of people and a lack of proper sanitary services: the London sewer system had not reached Soho. Cowsheds, slaughter houses, and grease-boiling dens lined the streets and contributed animal droppings, rotting fluids and other contaminants to the primitive Soho sewer system. Many cellars had cesspools underneath their floorboards, which formed from the sewers and filth seeping in from the outside. Since the cesspools were overrunning, the London government decided to dump the waste into the River Thames, contaminating the water supply. London had already suffered from a "series of debilitating cholera outbreaks". These included outbreaks in 1832 and 1849 which killed a total of 14,137 people.
John Snow (15 March 1813 – 16 June 1858) was an English physician and a leader in the adoption of anaesthesia and medical hygiene. He is considered one of the fathers of modern epidemiology, in part because of his work in tracing the source of a cholera outbreak in Soho, London, in 1854. His findings inspired fundamental changes in the water and waste systems of London, which led to similar changes in other cities, and a significant improvement in general public health around the world."
- Wikipedia