My understanding is that, if you take fluoride out of the water, you’ll need to replace it with something or the water will replace it itself (aka eat the pipe).
That obviously doesn’t mean fluoride was originally added for that reason though.
I doubt most freshwater sources have enough minerals in them to not be corrosive enough to need to add anything to reduce corrosiveness (ground water wells, rivers, etc...). The only purpose for adding fluoride would be to add fluoride for dental purposes.
The only thing I could think of that might have corrosive issues would be desalination water that was overly purified like the sibling comment mentioned. But even then, they should be adding some kind of minerals back before distributing it to people's homes. Ultrapure water tastes horrible and likely isn't safe for drinking long term.
I haven’t been able to find a source since posting this. I may have my facts backwards! The closest I have is this CDC report saying it reduces corrosiveness: https://www.cdc.gov/fluoridation/engineering/corrosion.htm
My understanding is that, if you take fluoride out of the water, you’ll need to replace it with something or the water will replace it itself (aka eat the pipe).
That obviously doesn’t mean fluoride was originally added for that reason though.