Between the 1860s and 1920, successive outbreaks of typhoid fever killed over 300,000 Americans. As population growth surged and people moved to urban areas en masse, American cities began to dump sewage in the same rivers that provided their drinking water. After epidemiologists linked typhoid outbreaks to water cleanliness, cities began building large-scale sand filtration systems in the 1890s, and in 1908, Jersey City pioneered the first continuous chlorination of a public water supply. By th...