What is Colour?

Colour is a measurement of the amount of colour units in a water sample.

How is Colour measured?

A common method for colour analysis is Method 110.2, the platinum-cobalt method. The colour of a water sample is visually compared to a sample with platinum-cobalt standards. Measurement is based on colour units, with one unit of colour being that produced by 1 mg/L platinum in the form of the chloroplatinate ion.

Why is Colour important?

For drinking water, colour is an important measurement for aesthetic purposes affecting the appearance and taste of the water. Colour in drinking water may result from coloured organic substances or natural metallic ions such as iron, manganese and copper. Colour causing organic substances are of particular concern due to their potential for disinfection by-product formation when they are combined with chlorine.

For industrial manufacturing, largely pulp and paper and textile industries, colour is often measured in the wastewater for removal purposes and effluent monitoring. Dyes and coloured organic substances are used extensively to add colour to various different substrates in the manufacturing process. The wastewater stream from these processes can contain a high level of colour which, if discharged untreated, can cause environmental problems, problems for downstream drinking water facilities, or wastewater treatment issues for wastes discharged to the sewer system.

Measuring Colour with UV-VIS technology

Due to the versatility of spectral analysis, colour can be measured accurately for both municipal and industrial applications with UV-VIS technology. For drinking water applications where colour primarily originates from decaying leaves and vegetation, using a single wavelength at 254 nm will often produce excellent correlations to colour units. Industrial applications that require detection of colour amidst a complex background will benefit from full UV-VIS scanning to isolate problematic dye signatures in the wastewater for accurate, real-time measurement.

Where is colour measured?

  • Influent to drinking water plant
  • Effluent of drinking water plant
  • Distribution system
  • Influent to industrial wastewater treatment plant
  • Effluent stream to environment or sewer system