The chromaticity of water is divided into two kinds: surface color and true color
Surface color refers to the color of the water without removing the suspended matter, including the color produced by the dissolved substances and insoluble suspended substances.
True color is the color of the water after the removal of suspended matter, produced only by dissolved colored substances.
Clean or very low turbidity of the water, the true color and table color is similar; coloring is very deep, more suspended matter industrial wastewater, domestic sewage two differences.
Water quality physical and chemical tests usually only determine the true color.
Clean natural water, in the water layer shallow for colorless transparent, deep when the light blue or light green.
Natural water often presents different colors is the decomposition of organic matter in water and contains inorganic substances caused by the most common is the color of organic complexes produced by the decomposition of natural organic matter.
For example, plant organic matter dissolved in water, the water will be pale yellow, or even brownish yellow; water containing high iron compounds is yellow; hydrogen sulfide in water is oxidized to precipitate sulfur, can make the water is light blue; some swamp water, because the plant contains tannic acid and gallic acid and iron into iron salts and black; the presence of a large number of algae in the water will be different colors due to the type of algae, such as chlorella to make the water is green, diatoms were brownish green, methanogamous algae were brownish green. Diatoms are brownish green, methanogens are dark brown, and blue-green algae are emerald; water polluted by industrial wastewater can show the color specific to the industrial wastewater.