There are two reasons for limiting the concentration of Manganese in drinking water: 

1) to prevent aesthetic and economic damage to property, and 

2) to avoid any possible physiological effects from excessive intake.

 The domestic water user finds that manganese produces a blackish color in laundered goods and affects the taste of beverages, including coffee and tea. The Pa. DEP limit for manganese is 0.05 mg/l.  Essentially the same treatment processes used to remove iron are used to reduce manganese levels. However, manganese is harder to remove than iron, because its precipitation is more pH dependent.