Public health institutions like the CDC and the ADA conclude that extensive research conducted has demonstrated that fluoridation of public water supplies is a safe and effective way to reduce the incidence of tooth decay in a community.
While exposure to high levels of fluoride over a long time can cause dental fluorosis, a condition that leads to mottled tooth enamel, discoloration, and in some cases erosion the gum line, the fluoride content in your drinking water is limited under federal law so the levels are very low.
In April 2015 the U.S. Department of Health and Human Services announced the final U.S. Public Health Service recommendation
for the optimal fluoride level in drinking water to be a single level of 0.7 milligrams of fluoride per liter of water. This recommended level replaced the previous recommended range (0.7 to 1.2 milligrams per liter) issued in 1962.