scope:

This International Standard specifies four methods for the examination of colour. The previously most employed for assessment of water colour in water treatment plants, limnological surveys etc. was based on the hexachloroplatinate scale [1]. The procedures in Clauses 6 and 7 are harmonised with this traditional procedure [2] and [4]. Clause 4 specifies a method for the examination of apparent colour by visually observing a water sample in a bottle. This gives only preliminary information, for example for use in field work. Only the apparent colour can be reported. Clause 5 specifies a method for the determination of the true colour of a water sample using optical apparatus and is applicable to raw and potable water and to industrial water of low colour. For interferences see 5.3. Clause 6 specifies a method for the determination of the true colour of a water sample using optical apparatus for comparison with hexachloroplatinate concentration at wavelength ë = 410 nm. For interferences see 6.2. Clause 7 specifies a method for the determination of the colour by visual comparison with hexachloroplatinate standard solutions and may be applied to raw and drinking water. For interferences see 7.2. The procedures in Clauses 4 and 5 are recommended if the colour hue of the sample differs from the hue of the matching solution. Under certain circumstances, strongly coloured water samples need to be diluted before examination or determination. However, this may alter the physical-chemical conditions leading to a change in colour. One purpose of the present revision is to forward the use of colour units (CU) instead of the traditional unit mg Pt l-1 which is often a cause of confusion, since the element Pt is hardly present in the sample When stating the result, it is absolutely necessary to refer to the applied procedure (Clauses 4 to 7).