Does community water fluoridation affect IQ? No.
/Several studies have examined the association between fluoride exposure and cognitive deficits and have found either no correlation or a correlation that is favorable toward cognitive outcomes.
For example:
Community Water Fluoridation and Intelligence: Prospective Study in New Zealand (2015)
This study published by the Journal of the American Academy of Public Health found no link between folk's IQ scores and growing up in a fluoridated community. Communities with water fluoridation had slightly higher IQ scores (on average), but the difference in IQ scores wasn't statistically significant.
Review the NTP Monograph on the Systematic Review of Fluoride Exposure and Neurodevelopmental and Cognitive Health Effects (2020)
The National Academies of Science, Engineering, and Medicine (NASEM) issued a report to evaluate a monograph, which concluded that fluoride was a neurotoxin. In its report, NASEM found that this conclusion was based on evidence with "a high risk of bias." According to NASEM, the claim is not supported by the evidence presented.
Toxicity of fluoride: a critical evaluation of evidence for human developmental neurotoxicity in epidemiological studies, animal experiments and in vitro analyses (2020)
A scientific review by the Archives of Toxicology of collected evidence does not support the claim that fluoride is a neurotoxin. This article, written by 31 experts in toxicology, neurology, and food safety, reviewed dozens of studies. The experts noted that "based on the totality of evidence," the review did not support "the presumption that fluoride should be considered as a human developmental neurotoxicant at current exposure levels" at the fluoride levels in Europe (very similar to the levels seen in the U.S).
The Effects of Fluoride In The Drinking Water
A study by economists (2016) in Sweden relied on an extensive data set of public health registers to investigate the relationship between fluoride and cognitive ability, using labor market outcomes (employment, etc.) as a proxy. The economists found that fluoride concentrations below 1.5 mg/L had "zero effects on cognitive ability, non-cognitive ability, and education," and they concluded that "fluoride improves labor market outcome later in life."
Fluorinated water consumption in pregnancy and neuropsychological development of children at 14 months and 4 years of age
Research from Spain presented orally at a European conference (2019) and featured in Environmental Epidemiology showed that prenatal exposure "at the levels found in fluorinated drinking water may exert a beneficial effect on the development at 4 years of age." Spain fluoridates several urban water systems. The authors are submitting their research to a peer-reviewed journal.
An Evaluation of Neurotoxicity Following Fluoride Exposure from Gestational Through Adult Ages in Long-Evans Hooded Rats
An animal study (2018) led by U.S. scientists at the National Toxicology Program (NTP) examined a possible fluoride-IQ link, and its authors "observed no exposure-related differences in motor, sensory, or learning and memory performance" on various tests. It's worth noting that leading critics of fluoridation pointed to this NTP research as the study that "could end fluoridation."
A Significant weight of the evidence shows that water is safe in communities adding fluoride.