Colour in Drinking Water Information:

Properties:

It is expected that drinking water is clear and clean; when water is tinged with brown, yellow, or red colours, consumers tend to worry and file complaints. Colour in water is caused by the absorption or reflection of light by suspended and dissolved particles; the more of these particles there are, the more colour is present in the water.1 The main sources of colour in water are humic and organic materials, iron complexes, and bacterial action on dissolved manganese particles. In general, colour in water does not pose a health risk for consumers; however, water that looks dirty is not readily accepted by those who drink it.

Sources:

Rivers, lakes, and other surface waters with high concentrations of decaying organic material are the most likely to be affected by colour. Fulvic and humic acids from soil and vegetation are examples of colour-causing compounds that are naturally sourced, and such organic matter can make water look dirty and yellow to brown in colour.1 Additionally, the degree of colouration in a raw water source can vary greatly with season and weather.2 If water looks red or brown, there may be high concentrations of iron-based compounds present. These come from old cast iron water pipes and mains as iron is released and oxidised.1 In some cases, bacteria associated with manganese can form oxides that cause water to appear black in colour.1

Regulations:

There are no regulatory standards for colouration in drinking water. Generally, action is taken if consumers are dissatisfied with the colour of their water.

Health/Environmental Concerns:

Colour in water is not necessarily harmful to human health. However, if raw water with high concentrations of organic material is treated with chlorine for disinfection, hazardous compounds called trihalomethanes (THMs) can form. In general, the main concern with colour in water is consumer objection and opinion rather than human health.3

Action:

Colour-causing organic matter can be removed during the water treatment process using methods such as ozone oxidation and activated carbon treatment.1 Filtration can also help to reduce a good deal of colour-causing contamination. Replacing cast iron mains and updating water storage and transportation structures can reduce discolouration caused by iron oxides. If you have concerns about the colour of your water, contact your Water Service Authority. If drinking water makes you feel ill, contact a doctor right away.

1 Guide to the Parameters in the European Communities. What’s in your water?; S. I. No. 278 of 2007; National Federation of Group Water Schemes: Ireland.

2 Issues with Your Water’s Colour: Water for Life, 2019. Southern Water Web site. https://www.southernwater.co.uk/help-advice/drinking-water-quality/issues-with-your-waters-colour (accessed Dec 31, 2019).

3 Interpretation and Standards. Parameters of Water Quality; 1-84096-015-3; Environmental Protection Agency: Ireland, 2001.