[chronicsonic]

“Water was collected from initially identified endemic fluoride regions according to the geological research of Government of India. “

Wonder why those areas were so fluoride endemic? First thought is factory waste running off into rivers?

[jfengel]

Some places naturally have water high in fluoride, due to the nature of the rocks and the water table.

That's how fluoride protection of teeth was discovered in the first place. People living in some parts of Colorado had mottled teeth from too much fluoride in the water. (It's now called "fluorosis".) Dentists noticed that such people also didn't get many cavities, and eventually tracked it to the composition of the water.

Turns out you can add enough fluoride to protect teeth without causing stains. Some places have way too much fluoride in the water. The staining appears to be the only problem.

[opwieurposiu]

In some areas fluoride is in the rocks and dissolves into the underground water. This is pumped up via wells.

Surface water, AKA rivers, starts with low fluoride in the mountains and it slowly accumulates as it flows down to the sea. Surface water almost always has less fluoride then well water though.