5.7.2 Organisms causing colour problems

Excessive growths of some algae, cyanobacteria and other bacteria can produce undesirable “blooms” in source waters, and this may affect colour in the distribution system.

Blooms of algae and cyanobacteria may be controlled by judicious application of copper sulphate or other algaecide to the source water. Any decision to use an algaecide needs to be discussed with the relevant health authority or drinking water regulator and be consistent with jurisdictional policy. Applications of algaecide can lead to the release of cyanotoxins from otherwise intact cells. Cyanobacteria and their toxins are discussed in detail in the relevant fact sheets in Part V.

When pigmented organisms such as cyanobacteria and algae are crushed on filters, colour problems can result. This type of problem can be exacerbated by the passage of microalgae through the filters causing an increase in turbidity.