What is a common cause of black stains on plumbing fixtures?

Black stains on plumbing fixtures are commonly caused by manganese. Manganese is a naturally occurring mineral found in soil and water, and when present in high concentrations, it can precipitate out of water and form black stains upon contact with air or surfaces. In plumbing systems, manganese can accumulate in pipes and fixtures, leading to these noticeable black stains, particularly if the water is acidic or has low oxygen levels that allow manganese to dissolve more readily.

Iron, calcium, and sodium do not typically produce the same black staining effect. Iron usually results in reddish-brown stains, calcium can leave white or cloudy deposits, and sodium does not cause visible staining at typical concentrations found in water supplies. Understanding the characteristics of manganese and how it interacts with plumbing materials helps in identifying and addressing the problem effectively.