Enough flouride to cause long-term health issues takes at least 2 mg/liter of water (probably more) over a long period of time, while artificially fluoridated water standards are 0.7 mg/liter. Even many rivers and lakes have a natural fluoride content of 0.3 mg/liter.

While there is risk from fluoridated water in some places, generally this is from unusally high natural fluoridation, from minerals leached from rock exposed by volcanic shifts or badly-regulated mining.