John Snow’s 1854 Broad Street investigation linked London’s cholera outbreak to the Broad Street pump. Snow mapped cases around Soho and observed that many affected residents had obtained water from that pump.
The outbreak began in August 1854 and caused hundreds of deaths in a short period. Snow argued that cholera was transmitted through contaminated water, opposing the prevailing miasma theory that blamed poisonous air. His evidence did not identify the bacterium directly, but it connected disease distribution with a shared water source.
Snow persuaded local officials to remove the pump handle, an action that became a famous episode in public-health history. The outbreak was already declining, so the intervention’s precise effect is difficult to measure, but the investigation helped establish epidemiology as a method based on mapped patterns and comparative evidence.
The pump water was contaminated by sewage, likely through a cesspit near the well. The episode did not mean every cholera outbreak had exactly the same source.