The water treatment plant adds it and monitors it.

You just reminded me that since I stopped drinking tap water a few years ago I’m not getting floridated water.

@JLeslie I mean do they throw a cup, of fluoride, in a vat of water, and stir it? Or something else?

It’s kept in a holding tank and then added to the water. There might be a youtube about it. I’m not sure if the water is in a holding tank or just running through the system.

They tip sodium fluoride into the water and let it dissolve.

If the water source is a reservoir, all you have to do is add fluoride to the reservoir. There is no need to stir. At the beginning, it will take a bit of time for the fluoride to disperse throughout the reservoir. After that, the fluoride will continue to be evenly distributed.

Where my grandmother grew up in Oklahoma, there was natural fluoride in the water. When she died at age 97, she had all of her own teeth and no cavities.