Water fluoridation not only affects tap water. Water fluoridation of tap water affects things like beer, soda, juices sold that are reconstituted from concentrate(most juices are that way), and any other food sold that uses water somehow. The reason for this is that all these products use tap water. Usually they filter the tap water however what they use to filter the tap water does not get the fluoride out.
Most bottled water is filtered in a way so that most fluoride is removed. This filtration method is called reverse osmosis. Reverse osmosis removes most of the fluoride but not all.