The Story of John Snow
The Father of Modern Epidemiology


This lesson comes to us from National Geographic. Check out the Full Lesson Here

We didn’t always clean our dirty water (and in many places around the world, we still don’t). In fact, most municipal sewer systems have only come about in the last few hundred years. The answer to why we clean our dirty water may seem obvious today, but not so long ago it was a complete mystery.

John Snow was innovative in his time for figuring out the connection between where people were getting sick, how disease might be spreading, and what could be done about it.

Today, we are applying many of those same strategies in our fight to contain the spread of SARS CoV-2, the coronavirus that causes Covid-19. In our time, like in John Snow’s, what we do with our dirty water may hold a key piece of information.


Cholera Deaths in Soho, London 1854

In London, England, during a ten-day period in the winter of 1854, 500 people suddenly died.

Everyone who perished all died of the same illness in a single section of the city. The cause of death was determined to be Cholera, a severe infection of the small intestine. 

What was the source of this disease and how was it spreading? A physician named John Snow was determined to find out. 

Dr. Snow began by drawing a map of the afflicted part of the city, a district called Soho. On this map he marked the home of each victim with a dot. 

Dr. John Snow was one of the first people to make the connection between our waste and our water. In 1854, running faucets and tap water were not available in homes. In many neighborhoods of London, people drew water from a local water pump and carried it to their homes. 

Dr. Snow had a guess that drinking water might be carrying the deadly cholera bacteria. So he drew a map of the pumps that supplied Soho’s drinking water to residents.


Pumping Stations In Soho London 1854

He noticed immediately that the cluster of deaths was located within walking distance of the Broad Street water pump.

Based on his findings, Dr. Snow convinced the London authorities to turn off the suspected water pump. The number of cholera deaths immediately declined to almost zero.

Because of his pioneering efforts, Dr. John Snow is considered the father of modern epidemiology, the study of how infectious disease spreads.

Dr. Snow found the connection of how Cholera was infecting humans, it came to them through their drinking water supplies. How Cholera was getting there in the first place remained a mystery for a while longer.

What was known at the time was that people disposed of their human wastes in chamber pots, since running water was not available in homes.

They would often discard the remnants out the window. Those wastes would then flow into the streets and into local creeks and rivers.

It was not widely understood in 1854 that the original source of the cholera was human feces. 


Wastewater Treatment Plants

We have been able to largely eradicate cholera deaths in the developed world by creating wastewater treatment systems.

These systems consist of a network of underground pipes all connected to a single treatment plant. They are designed to keep our drinking water and our wastewater separate.

These systems also clean our dirty water in order to remove human wastes and any number of infectious microorganisms that travel with it, from our water supplies in the process.

Because these systems regularly collect a community’s waste (and the infectious diseases that may be there as well), they can tell us a lot about our community’s health.

Through active monitoring and testing, we are able to use these same systems as a tool to monitor the spread of infectious disease. Particularly SARS-CoV2, the coronavirus responsible for Covid-19. 


Additional Resources

  • To View an Interactive GIS version of These Maps, Check out the ESRI MAP HERE. Select “Details” in the upper right hand corner. Then select “Content” and toggle on “Snow Map” and “Public water pumps.”
  • To learn more about John Snow and how his work reverberates today, CHECK THIS OUT