This International Standard specifies four different methods, designated A to D, for the examination of colour: - A: visual examination; - B: determination of the true colour using optical instruments at wavelength λ= 436 nm, λ= 525 nm and λ= 620 nm; - C: determination of true colour using optical instruments for determination of absorbance at wavelength λ= 410 nm; - D: visual method for the determination of the colour in natural water using a comparator. The previously most employed method for assessment of water colour in water treatment plants, limnological surveys, etcetera, was based on the hexachloroplatinate scale. Methods C and D are harmonized with this traditional procedure. Method A involves a method for 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. Method B involves a method for determination of the true colour of a water sample using optical apparatus. It is applicable to raw and potable water and to industrial water of low colour. See corresponding clause for interferences. Method C involves a method for determination of the true colour of a water sample using optical apparatus for comparison with hexachloroplatinate concentration at wavelength, λ = 410 nm. See corresponding clause for interferences. Method D involves a method for determination of colour by visual comparison with hexachloroplatinate standard solutions and can be applied to raw and drinking water. See corresponding clause for interferences. Methods A and B are recommended if the colour hue of the sample differs from the hue of the matching solution. Under certain circumstances, strongly coloured water samples require dilution before examination or determination. However, this can alter the physical-chemical conditions leading to a change in colour. An internal quality control procedure for all methods specified in this International Standard is described in Annex A. Precision data are given in Annex B. When stating the result, the procedure used (methods A to D) shall also be implicitly stated. This standard differs from DIN EN ISO 7887:1994-12 as follows: a) a new method has been included. - Method C: Determination of true colour using optical instruments for determination of absorbance at wavelength λ = 410 nm; b) precision data for selected matrices for the following methods have been included: - B: determination of true colour using optical instruments, - C: determination of true colour using optical instruments for determination of absorbance at wavelength λ = 410 nm, - D: visual determination of the colour in natural water using a comparator; c) the standard has been editorially revised. This document has been prepared by Technical Committee ISO/TC 147 "Water quality" in collaboration with CEN/TC 230 "Water Analysis", the secretariat of which is held by DIN (Germany). The responsible German committee is NA 119-01-03 AA "Wasseruntersuchung" ("Water Analysis") at the Water Practice Standards Committee (NAW).