Fluoride is an element that is found naturally occurring in drinking water or may be added into drinking water supplies as a public health measure to reduce the risk of cavities. The level of fluoride in drinking water has been of concern as excess fluoride has been associated with fluorosis (mottling and pitting of tooth enamel), bone fractures and skeletal fluorosis, a painful and sometimes crippling condition. There may also be a link between fluoride exposure and osteosarcoma (bone cancer), neurotoxicity and disruption of thyroid function.
The EPA has developed a fact sheet that reviews EPA’s position on fluoridation of water, some of the controversies, and possible health effects. Read: Questions and Answers on Flouride
From Environmental Working Group: Fluoride in Tap Water – What you can do