If you have well water, it may not have naturally occurring fluoride, but if you live near a volcano and there are wells in the area, they may contain natural fluoride. It is always advisable to test well water regularly.
For example,
Crystal Geyser water is naturally fluoridated because the source of that water is volcanic.
The process of Reverse Osmosis helps to get rid of some of the fluoride added to municipal water, but not all of it.
Here is a link that shows the level of natural fluoride contamination in Texas waters:
http://www.fluoridealert.org/wp-content/pesticides/levels/texas.htmlIn Turkey, some waters are very high in flluoride, which causes bone and tooth problems.