Water fluoridation remains the most effective, reliable, convenient, and cost-effective method of providing fluoride to the population, since it does not depend on individual compliance. The “optimal level” is related to a geographic area’s average temperature. This is usually 1 part per million (ppm), which is equivalent to 1 mg of fluoride in 1 liter of water. Many areas of the country have naturally occurring fluoride in the water supply, especially in the Midwest and Southwest. This has led to a higher incidence of fluorosis, or mottled teeth, because of the overingestion of fluoride. Therefore it is imperative to have private well water tested for fluoride levels before fluoride supplementation.