You probably don't have to worry about fluoride, and a very small amount might be good for you. This may not be the popular opinion in this forum, but I'll explain my reasoning. Many many natural water sources contain fluoride. Our body probably evolved a way to process it, and I would guess that some fluoride would actually be beneficial (in addition to preventing cavities). Yes I'm aware that there's a study that showed areas in China where they water had 3x the EPA limit of fluoride had children with lower IQ. There are also many other studies showing links (correlation, not causation) to fluoride and many bad things. So yes I believe there is an upper limit. But I also think there could be an optimal intake amount. I just don't think it would be worth the risk of approaching the upper limit trying to shoot for the optimal amount.
The biggest problem with fluoride is that a normal person will drink it, bath in it, then use fluoridated toothpaste and mouth wash. If you don't do any of those things I don't think you need to worry about trace sources such as in salt, or in washing your clothes in fluoridated water.
The reason I though about it so much is I was thinking about getting some grass fed bones to make broth, but I was worried about the fluoride. After all almost every municipal source of water is fluoridated. It turns out that the municipality where the cows are raised (St. George, UT) doesn't, but they still measure. Their fluoride levels were 2.6 whatevers per thingies compared to 7.3 whatevers per thingies of fluoridated water. So I realized even if the cows went to a completely pollution free natural water source they would still intake fluoride. So I concluded you can't eliminate all sources of fluoride, and although I'll never be able to prove it you probably wouldn't want to. So just don't drink tap water or use regular toothpaste and mouth wash and don't worry about the fluoride content of anything else.