Manganese is a naturally occurring metal used in steel and aluminum alloys. It is also an additive in unleaded gasoline, pigments, plumbing materials, battery cells, matches, fireworks, and fertilizer. High levels of manganese can stain fixtures and clothing and there may be a metallic taste to your water. At high levels, it can change water to a brownish-red color. Exposure to high concentrations of manganese over many years has been associated with toxicity to the nervous system.