Science Matters

The story of John Snow and the pump handle

Boyce Rensberger

(5/2025) In August and September of 1854, the Soho neighborhood of London was experiencing a horrible outbreak of cholera. It’s a debilitating, diarrheal disease that can kill within days if left untreated.

Cholera, rarely seen in the developed world these days, has ravaged cities for thousands of years. Epidemics were often blamed on bad air, called miasma, that anyone might inhale. In the mid-1800s, cholera killed tens of thousands of Britons every year. In the United States, cholera killed thousands each year during the same decades.

In 1854 London a local doctor named John Snow (no relation to the character in "Game of Thrones") was skeptical of the prevailing miasma explanation. He thought it could be bad water instead.

Snow had grown up poor in York and witnessed a local river contaminated by sewage carrying human waste. As a teenager he was apprenticed to a "surgeon-apothecary" for six years. Snow resolved to become a doctor and graduated from the University of London in 1844. He quickly gained a reputation as an excellent physician specializing in anesthesia for the surgery that was becoming more commonplace. He was appointed personal anesthetist to Queen Victoria, giving her chloroform during the births of her last two children.

But during that late summer in 1854, Snow turned his attention to the growing cholera outbreak in London. In one week of September, it killed some 600 people in a fairly small part of the city. Something about the deaths caught Snow’s attention. Many of them were concentrated in one part of Soho.

Snow got the idea of plotting their locations on a map. Then he noticed that near the center of the victims’ homes was the Broad Street water pump where most people got their water. This, of course, was in the days before ordinary homes had running water.

On a hunch, Snow had the pump handle removed, forcing people to go father, to other waterworks. Within days, cholera deaths dropped almost to zero. Buttressing Snow’s blame of dirty water was his observation that some nearby neighbors were untouched by cholera. They were workers at a brewery and a poorhouse, both of which had their own wells and did not use the public water supply.

John Snow had discovered a natural experiment that included an experimental group (those using the Broad Street pump) and a control group (those using their own wells). Snow didn’t discover what it was in the water, but his observations and his reasoning made a strong case for cholera being caused by a contaminant in drinking water.

Soon after Snow’s discovery physicians and political leaders began to think that other diseases might be caused by something in the environment that afflicts whole groups of people. And they thought those diseases might be alleviated by studying not just individual victims but the conditions that surround them. The study of such matters came to be called public health,

Benjamin Disraeli, who would later become prime minister, along with other members of Parliament, created the Thames Authority. That river was the source of most of London’s water, some pumps pulling water from within the city and others tapping farther upstream where the water was likely to be cleaner. Parliament passed legislation forcing the overhaul of the city’s water and sewage systems. Soon after that, there were no significant cholera outbreaks.

Two years after the pump handle incident, Britons established what is now called the Royal Society for Public Health.

The episode of John Snow and the pump handle is widely regarded as the genesis of a new field of science called epidemiology—literally the science that studies epidemics. I would guess that every trained epidemiologist in the world knows the story. (I’ll tell you why I think that in a minute.) Snow also established the basic methodology used by modern public health workers to investigate infectious disease outbreaks. His work helped confirm the validity of Germ Theory, which was still controversial in his day.

Today there are several statues and monuments around Britain dedicated to John Snow. A memorial pump with no handle stands near the site of the original.

Less celebrated in the annals of public health is another Englishman, Edwin Chadwick. A lawyer and head of the Poor Law Commission, his studies of how the poor lived—linking short life expectancies to squalid environmental conditions—launched what came to be called the "sanitary movement."

In the United States that movement eventually led the federal government to create what would eventually be called the Center for Disease Control and Prevention, known as the CDC. The agency’s first mission in 1946 was to keep malaria from spreading across the country. Yes, we used to have malaria here, mainly in the deep south. That’s why the CDC was stationed in Atlanta. If you don’t worry about catching malaria when you go to Florida or New Orleans, you can thank the CDC.

Over the ensuing decades it has become the most celebrated institution of public health in the U.S. and, arguably, worldwide. CDC is our leading public health protector against measles, E. coli, polio, smallpox, HIV/AIDS, Ebola, SARS, Zika, pandemic influenza, and COVID-19 among many other diseases—including cholera, which still strikes in some parts of the world.

For nearly 80 years the CDC’s "disease detectives"—epidemiologists, infectious disease specialists, and other experts—have been patrolling the country to catch disease outbreaks before they spread too far. And they have been scouring the world to spot and control outbreaks before they can reach our shores.

Not only have CDC employees been doing these things, but they have also been training others—70 to 80 each year, selected from more than 400 applicants—in the best methods for doing these things. State health departments send people for training. Other countries send their top health workers. They spend one month at the headquarters in Atlanta and the next 23 months interning with trained disease detectives around the country or in their home country.

Graduates join CDC’s Epidemic Intelligence Service, part of a global network of EIS Officers who work collaboratively to keep their respective publics safe and healthy.

So, it is more than saddening to see an ignorant president allow a deluded secretary of health and human services to tear down the CDC. Some 1,300 CDC employees have been fired in recent weeks, including all 50 of the newest class of EIS Officers in their first year of internship plus some in their second years. More than saddening.

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