<P> Much of the early work on establishing the connection between fluoride and dental health was performed by scientists in the U.S. during the early 20th century, and the U.S. was the first country to implement public water fluoridation on a wide scale . It has been introduced to varying degrees in many countries and territories outside the U.S., including Argentina, Australia, Brazil, Canada, Chile, Colombia, Hong Kong, Ireland, Israel, Korea, Malaysia, New Zealand, the Philippines, Serbia, Singapore, Spain, the UK, and Vietnam . In 2004, an estimated 13.7 million people in western Europe and 194 million in the U.S. received artificially fluoridated water . In 2010, about 66% of the U.S. population was receiving fluoridated water . </P> <P> Naturally fluoridated water is used by approximately 4% of the world's population, in countries including Argentina, France, Gabon, Libya, Mexico, Senegal, Sri Lanka, Tanzania, the U.S., and Zimbabwe . In some locations, notably parts of Africa, China, and India, natural fluoridation exceeds recommended levels . </P> <P> Communities have discontinued water fluoridation in some countries, including Finland, Germany, Japan, the Netherlands, and Switzerland . On August 26, 2014, Israel stopped mandating fluoridation, stating "Only some 1% of the water is used for drinking, while 99% of the water is intended for other uses (industry, agriculture, flushing toilets etc .). There is also scientific evidence that fluoride in large amounts can lead to damage to health . When fluoride is supplied via drinking water, there is no control regarding the amount of fluoride actually consumed, which could lead to excessive consumption . Supply of fluoridated water forces those who do not so wish to also consume water with added fluoride . This approach is therefore not accepted in most countries in the world ." This change was often motivated by political opposition to water fluoridation, but sometimes the need for water fluoridation was met by alternative strategies . The use of fluoride in its various forms is the foundation of tooth decay prevention throughout Europe; several countries have introduced fluoridated salt, with varying success: in Switzerland and Germany, fluoridated salt represents 65% to 70% of the domestic market, while in France the market share reached 60% in 1993 but dwindled to 14% in 2009; Spain, in 1986 the second West European country to introduce fluoridation of table salt, reported a market share in 2006 of only 10% . In three other West European countries, Greece, Austria and the Netherlands, the legal framework for production and marketing of fluoridated edible salt exists . At least six Central European countries (Hungary, the Czech and Slovak Republics, Croatia, Slovenia, Romania) have shown some interest in salt fluoridation; however, significant usage of approximately 35% was only achieved in the Czech Republic . The Slovak Republic had the equipment to treat salt by 2005; in the other four countries attempts to introduce fluoridated salt were not successful . </P> <P> The history of water fluoridation can be divided into three periods . The first (c. 1801--1933) was research into the cause of a form of mottled tooth enamel called the Colorado brown stain . The second (c. 1933--1945) focused on the relationship between fluoride concentrations, fluorosis, and tooth decay, and established that moderate levels of fluoride prevent cavities . The third period, from 1945 on, focused on adding fluoride to community water supplies . </P>

Where does the fluoride in our drinking water come from