Fluoride was first added to drinking water for the purpose of keep prisoners submissive in concentration camps.
The first occurrence of fluoridated drinking water on Earth was found in Germany's Nazi prison camps. The Gestapo had little concern about fluoride's supposed effect on children's teeth; their alleged reason for mass-medicating water with sodium fluoride was to sterilize humans and force the people in their concentration camps into calm submission. (Ref. book: "The Crime and Punishment of I.G. Farben" by Joseph Borkin.)… USAF Major George R. Jordan testified before Un-American Activity committees of Congress in the 1950's that in his post as U.S.-Soviet liaison officer, the Soviets openly admitted to 'Using the fluoride in the water supplies in their concentration camps, to make the prisoners stupid, docile, and subservient.
<EDIT> According to some replies, there is no citation in the book noted,The author focuses exclusively on sodium fluoride. However, about 91% of municipalities use industrial grade hexafluorosilicic acid as the fluoridating agent. While sodium fluoride is extremely toxic and deleterious to the human body, hexafluorosilicic acid is even worse.