The most common cause of water color is the presence of minerals.
Red and brown colors are due to iron,
Black to manganese or organic matter and
Yellow to dissolved organic matter such as tannins.
The true color of water is considered to be only that attributable to substances in solution after the suspended material has been removed. However, the color of water with low turbidity is substantially the same as that of clear water. The term “apparent color” is used for color that includes the effect from suspended material.
If required, suspended material should be removed by centrifuging. Filtration has a decolorizing effect and should not be used to remove suspended matter.
The unit of color considered as a standard is the color produced by the platinum cobalt method of measurement where one unit of color equals one milligram per liter of platinum in water. The results are conventionally expressed as units of color, not concentration (mg/l).
The source of color in natural water may be of natural mineral or vegetable origin. Color can be caused by minerals containing metallic substances, such as iron and manganese compounds and organic compounds such as humus material, peat, tannins, algae, weeds and protozoa.
The significance of color in domestic water is undesirable from aesthetic considerations and also because it may dull clothing or stain food and household fixtures.
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