Fluoride is commonly found in trace amounts in most soil and rock. Groundwater usually contains fluoride ions dissolved from geologic formation while surface waters generally contain smaller amounts, under 0.3 mg/L. The EPA has set the maximum contaminant level for fluoride at 4 mg/L to protect from bone disease. A secondary standard of 2 mg/L has been set to prevent dental disease of fluorosis (a discoloration of teeth). On the other hand, an absence or low concentration of fluoride in drinking water results in a high incidence of dental caries in children’s teeth. Medical studies have also indicated that fluoride benefits older persons by reducing the prevalence of osteoporosis and hardening of the arteries. The optimum fluoride concentration in drinking water, protects teeth from decay without causing noticeable fluorosis. Recommended limits are based on air temperature, since this influences the amount of water ingested by people.
Cities with water supplies deficient in natural fluoride, provide supplemental fluoridation to optimum levels to reduce the rate of dental decay in children. The fluoride compounds most commonly applied in water treatment are sodium fluoride, sodium silicofluoride, and fluosilicic acid. Application of fluoride is best in a channel or water main coming from the treatment plant. If no treatment plant exists, fluoride can be injected into the mains carrying water to the distribution system.
Water Supply and Pollution Control (Eighth Edition) 2009
By: Warren Viessman, Jr; Mark J. Hammer; Elizabeth M. Perez; Paul A. Chadik