Fluoride is a mineral added to water to prevent tooth decay. It occurs naturally and in industrial waste. High levels can cause tooth discoloration in children.

Fluoride occurs naturally in water as it passes through fluoride-containing rocks and soil. It's also released from industrial processes like aluminum and fertilizer production. Since the 1940s, many water systems have added fluoride to reach optimal levels for preventing tooth decay. Fluoride is measured in parts per million (ppm) using laboratory analysis. While beneficial at low levels, excessive fluoride intake can lead to dental fluorosis. The practice of water fluoridation remains controversial in some communities due to differing views on its necessity and safety.