Manganese occurs naturally as a mineral from sediments and rocks, or from mining and industrial waste. Manganese, even though not a toxic compound is a mineral which creates aesthetic and economic damage (concerns of brownish stain to laundry, negatively affects tastes of water and causes dark brown and/or black stains on plumbing fixtures). And although manganese is relatively non-toxic to animals, it can be highly toxic to plants at high levels. And, though not required for monitoring under S.D.W.A (Safe Water Drinking Act), many Public Water Systems (PWS) independently conduct monitoring and self regulation.
Data shown, that approximately 68% of all PWS served from groundwater (or an estimated 40,000 systems nationally) had detections of significant amounts of manganese affecting about 35% of the ground water PWS population, (or approximately 47.5 million people) around the US.
Source: WHO, “Manganese in Drinking Water,” 2004, p4.