Surface and ground waters rarely contain more than 1 mg/L of soluble or suspended manganese.  Manganese can act as an oxidizing or reducing agent depending on its valence state.  In various forms, it is used as a pigment or a bleaching agent.  Manganese concentrations in potable water should not exceed 0.05 mg/L.  The National Secondary Drinking Water Standard for manganese is o.o5 mg/L, as higher concentrations will impart a foul taste to water and discolor laundry and porcelain surfaces.  Levels higher than 1 mg/l in surface waters can result from mining operations or excessive discharging from domestic waste treatment facilities or industrial plants.

The Colorimetric Method.
CHEMetrics' tests measure soluble manganese compounds but do not differentiate the various valence states.  Manganese is oxidized in the presence of periodate to form a deep-red reaction product.    Results are expressed as ppm (mg/L) Mn.