It's hard to avoid in the United States. A simple carbon filter won't remove flouride from tap water. You need reverse osmosis.
Then, pretty much every single canned and bottled drink sold in America is made with flouridated tap water, so you would have to avoid beer, soft drinks, even all the drinks marketed as healthy.
I'm on well water so I don't have to worry about my tap water but I know I'm getting dosed with all the canned beverages I drink daily.
