Water fluoridation
Health and dental organizations worldwide have endorsed its safety and effectiveness. Its use began in 1945, following studies of children in a region where higher levels of fluoride occur naturally in the water. Further research showed that moderate fluoridation prevents tooth decay.
Drinking water supply and sanitation in the United States
In 1854, the British physician John Snow found that cholera was spread through contaminated water. As a result of his findings, several cities began to treat all water with sand filters and chlorine before distributing it to the public. Before efforts to clean drinking water were implemented at the turn of the 20th century, mortality among 1- to 5-year-olds in the United States in some major river cities was nearly one in five. Clean water is estimated to have reduced about three-fourths of infant mortality, and two-thirds of child mortality. By 1900, sand filtration was widely used. In 1908, the first continuous application of chlorination to drinking U.S. water was in Jersey City, New Jersey (and not without controversy). Cities also began to construct sewers. As a result of water treatment and sanitation, the incidence of cholera and typhoid rapidly decreased. Slow sand filtration was initially the technology of choice for water treatment, later being gradually displaced by rapid sand filtration.