In 1854, English physician John Snow made a significant breakthrough in understanding cholera and its transmission, which bolstered sanitation movements. Amid a deadly cholera outbreak in London, Snow challenged the prevailing belief that the disease spread through “miasma” or bad air. Through careful investigation and mapping of cholera cases, he traced the outbreak to a contaminated public water pump on Broad Street. By removing the pump handle, Snow effectively stopped the outbreak.

Snow's work provided compelling evidence that cholera was waterborne, not airborne, and underscored the need for clean water supplies and proper sanitation. Snow’s findings helped pave the way for modern public health reforms, leading to improved urban sanitation and the eventual eradication of cholera in many parts of the world.