Fluoride was first introduced into the drinking water of residents of Grand Rapids, Michigan in 1945 for the prevention of dental caries. Ever since, growing numbers of communities favor fluoridation. Now, over 7000 communities in the United States are adding F(0.7~1.2ppm) to their drinking water. The most effective to prevent tooth decay is putting lower concentrated fluoride(F, 0.7~1.2ppm) into drinking water. However, exact fluoride injection amount have not been decided, because the research of the fluoride injection effect was insufficient. Therefore, after separating fluoridation and non-fluoridation into public water supplies, we investigated concentration of fluoride, alkalinity, Al, Ca, Mg, evaporation residuals in APT, domestic, commercial area. Then, we decided allowable concentration of fluoride, injection point of fluoride in water supply system, cost effectiveness.