Water fluoridation depends upon:

Water fluoridation depends on the temperature in that area and body weight. Galagan formula for fluoride:  This is usually calculated by the formula given by Galagan and Vermillion in 1957. Ppm of F ‾= - 0.038 +0.0062 t temperature in Fahrenheit. ‘E’ is the estimated daily water intake for children in ounces per pound of body weight. ‘t’ is the yearly mean of the daily maximum temperature in Fahrenheit. Essentials of preventive and community dentistry  Soben Peter  5th edition