First, three procedural points:

1. You're presumably talking about the HHS review in your adjacent comment. Here's the actual monograph[1]. Notably, the review's authors consider it a "medium confidence" finding. In the NTP's taxonomy[2], that makes it a lower impact conclusion than the voluminous findings that show that fluoridation at 1.5mg/dL (much less 0.7mg/dL) has no adverse developmental effects.

2. The monograph is explicit about the limitations of its conclusions. In particular, the monograph explicitly says that it doesn't offer a quantitative account of fluoride-for-lost-IQ-points, and explicitly concludes that its findings do not address fluoridation at levels used in the US or Canada.

3. The monograph is focused on fluoridation at or above 1.5mg/dL, with extensive consideration given to much higher fluoridation levels.

As a whole, the monograph doesn't not present the cohesive, "closed case" for a relationship between municipal water fluoridation and developmental risk that you're suggesting exists. At best, it presents a body of evidence showing a moderate correlation between negative developmental effects and natural/dietary fluoride consumption at levels that are 5-10x times the level introduced in the US.

> If the standard is half the "safe" level, but some people consume 4x or 10x as much tap water, & perhaps even have a higher baseline of non-tap-water flouride consumption, then some percentage N of the population could developmentally-harmed, even at levels "safe" for "most".

First: neither your source (nor any source I'm aware of) shows developmental effects in adults, i.e. a general population sampling. Not even at extremely high naturally occurring fluoride levels.

However, even if we reduce to children, neither your source (nor any I'm aware of) shows a multiplicative effect to fluoridated water consumption. In other words: children in areas with 5mg/dL of naturally occurring fluoride appear to have blood levels that consistently correlate with that natural level, regardless of variations in dietary patterns. The parsimonious explanation for this is that fluoride doesn't bioaccumulate in soft tissues and is mostly excreted when not accumulated in teeth and bones, which research supports[3].

The TL;DR for this is that there's no positive evidence (and a lot of negative evidence) for differences in consumption during normal human activity having any effect on blood/urine fluoride levels. Baseline changes result in changes; volume does not.

(This ties in with the earlier point: you can definitely increase the amount of fluoride in your system over a point in time by, say, drinking 3 cups of green tea in a row. But children aren't doing that, and their most accessible equivalent - drinking water - is not something that they can chug liters of at a time.)

> Roughly, instead of one cavity-affected-tooth per 17 kids, there's one cavity-affected-tooth per 9 kids.

I personally wouldn't describe that kind of reduction as modest. On the city scale, that's thousands of dental procedures averted per year. Factored with differences in dental care (e.g. childhood cavities correlating with worse adult dental outcomes), and you have an expensive, easily preventable public health problem.

> What if we shifted the flouridation expense into reminding kids to brush or use a flouridated rinse?

Brushing reminders and basic dental hygiene are exceedingly well-messaged in developed countries. Despite that the problem remains, as evidenced by studies consistently showing differences between fluoridated and un-fluoridated populations with generally good dental practices[4].

I suppose we could always spend more on educating parents and children on good dental hygiene. But municipal fluoridation is cheap, effective, and most importantly pervasive: it addresses the last X% of the population that can't or won't practice good dental hygiene.

[1]: https://ntp.niehs.nih.gov/sites/default/files/2024-08/fluori...

[2]: https://ntp.niehs.nih.gov/sites/default/files/ntp/ohat/pubs/...

[3]: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7261729/

[4]: https://onlinelibrary.wiley.com/doi/10.1111/cdoe.12685