when did they start putting fluoride in water
1945
Water fluoridation
The third period, from 1945 on, focused on adding fluoride to community water supplies.
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Water fluoridation [SEP] History
The history of water fluoridation can be divided into three periods. The first () 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. In the first half of the 19th century, investigators established that fluoride occurs with varying concentrations in teeth, bone, and drinking water. In the second half they speculated that fluoride would protect against tooth decay, proposed supplementing the diet with fluoride, and observed mottled enamel (now called severe dental fluorosis) without knowing the cause.