Page 7: Guidelines for Canadian Drinking Water Quality: Guideline Technical Document – Colour

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Rationale

1. Colour in drinking water may be due to the presence of coloured organic substances; the presence of metals such as iron, manganese and copper; or the presence of highly coloured industrial wastes, the most common of which are pulp and paper and textile wastes. Although the presence of colour in drinking water may be indirectly linked to health, its primary importance in drinking water is aesthetic. Experience has shown that consumers whose drinking water contains aesthetically displeasing levels of colour may seek alternative, possibly unsafe, sources.
2. Levels of colour above 15 TCU can be detected in a glass of water by most people.
3. The aesthetic objective for colour has therefore been set at ≤ 15 TCU. The provision of treated water at or below this limit will ensure rapid notification by consumers should problems leading to the formation of colour arise in the distribution system. In addition, interferences by colour in water treatment processes and analytical procedures will be diminished. The removal of excess colour prior to chlorination will also reduce the production of trihalomethanes. Finally, limiting the colour in potable water will limit the concentrations of undesirable substances that may be complexed with or adsorbed to organic colouring agents.

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