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How did polluted water become linked to cholera in the 19th century?

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Diagram of a water treatment plant showing the process from water inlet through mixing, coagulation, flocculation, settling, filtering, chemical treatment with chlorine, storage, and high-lift pumping to the distribution system. — water purification Water from inlets located in the water supply, such as a lake, is sent to be mixed, coagulated, and flocculated and is then sent to the waterworks for purification by filtering and chemical treatment. After being treated, the water is pumped into water mains for storage or distribution.

In the 19th century, the link between polluted water and cholera was established primarily through the pioneering work of English physician John Snow. During the 1854 cholera epidemic in London, Snow challenged the then-dominant miasma theory, which incorrectly attributed disease to "bad air" arising from decaying organic matter.123

Snow proposed the radical view that cholera was transmitted through germ-contaminated water. He provided evidence for this by mapping cholera deaths in the Soho district, which clustered around a specific public water pump on Broad Street. He further strengthened his case with his "Grand Experiment," a study comparing cholera mortality rates among residents served by two different water companies: one drawing water from sewage-polluted sections of the River Thames and the other from a cleaner, upstream source.123

While Snow’s observations were initially met with skepticism, they were later validated in the 1880s when Robert Koch identified the causative bacterium, Vibrio cholerae, and confirmed the germ theory of disease. This discovery provided the scientific foundation for modern water purification and sanitation practices.24