Test Method Technical Information


Tests For: Colour in natural and treated waters
Test Range: 10–500 mg/L Pt (10–500 Hazen Units)
Basis of Test Method: Standard Method 2120-C, US EPA ref. 110.2

Testing for Colour

Pure water exhibits a light blue colour when viewed in depth. This colour may be modified by the presence of organic material, typically to a yellow or brown colour. An estimate of this colour intensity is used as a simple means of monitoring natural and treated water.

Test Method

The colour of the water is determined photoelectrically using the Palintest Photometer. The sample should be filtered to remove suspended solids before analysis to determine the ‘true colour’ due to dissolved matter.

The colour of water is expressed using the platinum/cobalt colour scale (Pt/Co scale). Each unit is equivalent to the colour produced by 1 mg/L platinum in the form of chloroplatinic acid in the presence of 2 mg/L cobaltous chloride hexahydrate. These units are identical with ‘Hazen’ units, which have been traditionally used to express results from the visual estimation of water colour.


Samples, which contain metallic impurities, dyestuffs or other industrial pollutants, may exhibit a different colour to the natural yellow-brown coloration. This test may not be suitable for samples of this type.