Has anybody examined the fluoride report by the National Toxicology Program? It apparently shows that only 0.7 mg/L (a typical amount in developed countries) is likely to correspond to an IQ loss of 3 points in children. This seems substantial.
Unofficial summary: https://ntp.niehs.nih.gov/sites/default/files/ntp/about_ntp/bsc/2023/may/publiccomm/neurath20230429_bsc_508.pdf
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"Many European countries have rejected water fluoridation, including: Austria, Belgium, Finland, France, Germany, Hungary, Luxembourg, Netherlands, Northern Ireland, Norway, Sweden, Switzerland, Scotland, Iceland, and Italy."
https://en.wikipedia.org/wiki/Water_fluoridation_by_country