Page 3: Guidelines for Canadian Drinking Water Quality: Guideline Technical Document – Colour
Occurance
Colour may occur in drinking water for any one or more of several reasons. It may be due to the presence of coloured organic substances originating in the decay or aqueous extraction of natural vegetation, such as in soil runoffFootnote 13; the presence of metals such as iron, manganese and copper, which are abundant in nature, are weathered from rock or corroded from distribution systems by water, and are naturally coloured; or the presence of highly coloured industrial wastes, the most common of which are pulp and paper and textile wastes.Footnote 14
At least 90% of the drinking water supplied to Canadian municipalities is obtained from surface water sources.Footnote 15 The colour of surface water is predominantly due to organic substances of natural origin.Footnote 1 In general, hard surface waters are less highly coloured than soft waters,Footnote 6 and the organic:inorganic ratio in the total dissolved solids content of soft water tends to be higher than that in hard water. The colour of groundwater is usually due to its coloured mineral content. In some areas, especially those associated with limestone stratification, the colour of groundwater from both shallowFootnote 1 and deepFootnote 16 wells may be organic in nature.
Date reviewed: 2026-06-05