Colour
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.
Most people can detect colour above 15 true colour units (TCU) in a glass of
water. Levels of colour below 15 TCU are often acceptable to consumers. High colour
from natural organic carbon (e.g. humics) could also indicate a high propensity to
produce by-products from disinfection processes. No health-based guideline value is
proposed for colour in drinking-water.