Drinking-water should ideally have no visible colour. Colour in drinking-water is usually
due to the presence of coloured organic matter (primarily humic and fulvic acids)
associated with the humus fraction of soil. Colour is also strongly infl uenced by the
presence of iron and other metals, either as natural impurities or as corrosion products.
It may also result from the contamination of the water source with industrial
effl uents and may be the fi rst indication of a hazardous situation. The source of colour
in a drinking-water supply should be investigated, particularly if a substantial change
has taken place.