Fresh or Raw Water

This can be colored, as turbid surface water may contain humus as well as iron and manganese, either in the oxidized form or bound to organic matter. Water of this type is treated by aeration + coagulation + addition of alkali + clarification + sand filtration. The removal of color and organic compounds usually requires a method based on chemical precipitation. Some reduction in organic matter content, of course, can be achieved by simple filtration. The removal of iron and manganese, on the other hand, usually requires  

Oxidation of iron (II) and manganese (II) to oxidation state III e.g. by chlorine or permanganate 

Hydrolysis of the trivalent cation to produce the hydrated hydroxide 

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