Water supplies in 18 villages in Tanzania had fluoride levels between 0.2 to 0.8 mg/L, which is higher than most natural sources, and US water typically contains 1 mg/L of fluoride.

“18 villages in four geographical areas had water supplies with 0.2 to 0.8 milligrams per liter of fluoride that's that's higher than most natural sources of water i could find but in the united states where most counties have fluoride in the water a lot of that water is one milligram per liter”