In the 1850s, cholera was a global scourge capable of devastating entire cities. When a particularly terrible outbreak hit the Soho neighborhood of London, Dr. John Snow realized that the outbreak centered around a certain water pump. Snow then noticed that rather than this being an isolated case, the fiercest outbreaks always seemed to focus around these water sources. By connecting the outbreaks to infected pumps, Dr. Snow was able to establish that cholera was spread by contaminated water—a landmark step towards eradicating its terrible effects.