Fluoride (F-) is an ion of the element fluorine, and is a natural component in most water resources. Fluoride concentrations in fresh water are generally less than 1 mg/L (milligrams per liter), and the concentration of fluoride in the world's oceans is about 1.3 mg/L. The source of most fluoride in natural fresh-water resources is various rocks and minerals in bedrock and sediments.
Because of fluoride's proven value in maintaining healthy teeth and bones, it is added to public water systems in Kentucky. The concentration in public water supplies is approximately 1 mg/L.
Although fluoride has a beneficial effect within a range of low concentrations, at higher concentrations it may cause fluorosis, which is indicated in more severe cases by brown staining or mottling of teeth. The U.S. Environmental Protection Agency has established a maximum contaminant level (MCL) for fluoride in public drinking water of 4 mg/L and a secondary, or aesthetic, standard of 2 mg/L. Some laboratories use a measurement unit of parts per million (ppm), which is essentially equivalent to mg/L in fresh water.
Utility companies that provide public water supplies test the water for concentrations of fluoride. This testing is much less common for private water supplies, however. More than 900,000 people in Kentucky use ground-water supplies, including approximately 500,000 supplied through public utilities, and at least 400,000 private wells or springs.
A map of the state shows the geographic distribution of fluoride concentrations, and a table shows the general trends of concentrations according to depth below the ground surface. Environmental scientists, engineers, and other professionals can use this information to gain an understanding of general trends in water quality that may be relevant on a regional or site-specific basis.