Manganese is a natural mineral comprising approximately 0.1% of the earth's crust. It is found in many salts and mineral complexes widely distributed in rocks, soils and at the bottom of lakes and oceans. For aquatic systems, the manganese (Mn2+) and manganic (Mn4+) oxidation states of manganese are the most important. The element dissolves in the water of some underground aquifers when present in the geological layers of the aquifer. Therefore, because groundwater contains manganese, it is present in well water distribution systems and drinking water supplies. A typical concentration of manganese found in groundwater is 2 mg/L (2 ppm). Manganese is generally present in natural surface waters, in dissolved or suspended form, at concentrations much lower than those in groundwater (less than 0.05 mg/L). The fact that it is more prevalent in groundwater supplies than in drinking water sources is attributed to reducing conditions that exist underground. Some lakes and reservoirs also contain high concentrations of manganese due to acid pollution.1.2 Impact on water qualityThe United States Environmental Protection Agency (EPA) has regulated a maximum contaminant level for manganese , not because this mineral is considered hazardous to health, but mainly due to aesthetic concerns such as staining effects, taste and discoloration. The recommended concentration limit for manganese in drinking water is 0.05 mg/L, set as an aesthetic objective (Health Canada, 2009). The presence of manganese in drinking water at high levels is undesirable, as it is associated with a range of problems. At concentrations above 0.15 mg/L, manganese stains plumbing fixtures and laundry. Additionally, it causes... middle of paper ...... manganese levels include hypertension, psychiatric illnesses, mental confusion, memory impairment, loss of appetite, and neurological problems. Well water containing high manganese content can lead to excess manganese consumption and increased bacterial growth (Blaurock-Busch, 2002). With the exception of an isolated incident, which is still unclear, no manganese poisoning due to drinking water has been recorded. In 1941, in Japan, the cause of an encephalitis-like illness was traced to well water with a high manganese concentration of 14 mg/L. However, other metals like zinc were also present in excessive concentrations and it was never confirmed whether the high manganese level alone was responsible for the illness. Concerning the acceptable daily intake, no adverse health effects have been observed in humans with the following daily intakes of manganese: