Fluoride exists naturally in water sources and is derived from the element fluorine. It is important in the prventation of tooth decay. If you use a well, fluoride levels should be checked by a laboratory. The optimal level of fluoride in the water supply are 0.9-1.2 ppm (parts per million). Your child's doctor or dentist may want to know whether your drinking water provides adequate levels of fluoride to combat tooth decay. If it does not, your dentist may recommend purchasing fluorinated bottled water.