The inside of my toilet bowl is stained black, what is going on with my water?
Black or brownish-black staining can indicate the presence of higher levels of manganese in water. Manganese, like iron, is a naturally occurring metal in soils and when found in water is not considered to be a human health hazard. However, manganese and iron in certain concentrations can impact the taste, color and odor of water and can stain porcelain fixtures, laundry and other household items. Manganese leaves brownish-black stains and iron will leave reddish-brown stains. The stains are not easily removed by common household cleaners and some may even intensify the stains. Manganese and iron deposits can also build up in pipes and other water fixtures throughout the house which can cause significant impact to your water system. If you notice staining or discoloration you should begin by having your water tested; those test results can then be used to determine appropriate treatment or mitigation options.
For more information on manganese and iron or other drinking water concerns visit: http://water.unl.edu/drinkingwater