In most places of the world, groundwater is the primary supply for a variety of uses. A significant problem is the presence of high concentrations of specific ions, which render groundwater unfit for use in a variety of ways. One such ion that affects people's health in more than 100 countries worldwide is fluoride. Groundwater contains varying amounts of fluoride, which can be attributed to either natural or man-made sources, or a mix of the two. Fluoride exposure has long-term effects on human health including skeletal fluorosis, which weakens and bends bones but also dental fluorosis, which causes teeth to turn brown, thus it's important to periodically check the amount of fluoride from groundwater sources and take action to get it down to the legally allowed range of 0.6–1.5 mg l−1. Fluoride can be extracted either in-situ or ex-situ from groundwater using a variety of techniques. However, the specific conditions of the area, such as the groundwater quality and the anthropogenic or natural cause of contamination, will determine which approach is best. Since fluoride contamination is a major and pervasive issue in many regions of the world with largely natural and preventable causes, public education and defluoridating groundwater before consumption are crucial for maintaining global health.