Fluoride not harmful
From a 2015 Surgeon General Report which took the information from the Center for Disease Control (CDC): The panel carefully considered public comments concerning fluoride in drinking water, including possible adverse health effects. As described in the updated guideline, the panel reviewed and accepted the scientific evidence in the 2006 NRC report on fluoride. Even at higher concentrations (i.e., 2–4 mg/L), the NRC found no evidence substantial enough to support claims of unwanted health effects, other than severe dental fluorosis. The NRC review noted that prevalence of severe dental fluorosis is nearly zero at fluoride concentrations <2 mg/L.