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.
Water fluoridation controversy
Public water fluoridation was first practiced in 1945, in the US. As of 2012, 25 countries have supplemental water fluoridation to varying degrees, and 11 of them have more than 50% of their population drinking fluoridated water. A further 28 countries have water that is naturally fluoridated, though in many of them there are areas where fluoride is above the optimum level. As of 2012 about 435 million people worldwide received water fluoridated at the recommended level, of whom 57 million (13%) received naturally fluoridated water and 377 million (87%) received artificially fluoridated water. In 2014, three-quarters of the US population on the public water supply received fluoridated water, which represented two-thirds of the total US population.