In the U.S., water companies add a small amount of fluoride -- between 0.8 and 1.2 milligrams per liter -- to drinking water as a way to protect teeth from decay. But in some parts of the world, including India, the Middle East and some African countries, water already has a lot of naturally-occurring fluoride, and the levels can be so high that they're dangerous to health. In one Indian village, for example, a naturally occurring level of 5 to 23 milligrams (.00017 to .008 ounces) per liter has caused residents to suffer severe anemia, stiff joints, kidney failure and stained teeth [source: World Health Organization].
Fortunately, Indian researchers offered a possible solution in a March 2013 International Journal of Environmental Engineering article. The researchers have developed a filter system that uses a common medicinal herb, Tridax procumbens, to absorb excess fluoride from drinking water. The plant, which has also been used to extract toxic heavy metals from water, attracts fluoride ions when water passes through it at a temperature of about 27 degrees Celsius (80.6 degrees Fahrenheit). The filter potentially could provide an inexpensive, easy-to-use way of making water safe in places where the supply contains excessive fluoride. But it also may be used by people in the U.S. and other countries who don't like the idea of fluoride being added to their water [source: Science Daily].