Large amounts of the organic compound Geosmin are responsible for residents experiencing a change in water taste or odour.
“Geosmin is a compound that is produced and released into the water bodies used for drinking water production by certain bacteria called cyanobacteria,” said Nonhlanhla Kalebaila of the South African Water Research Commission.
The naturally occurring compound is being drawn from dams and is not dangerous but can result in an unpleasant or “earthy” taste.
A source from the engineering department of the Stellenbosch Municipality, who asked to remain anonymous, said residents may be experiencing the effects of Geosmin from reservoir water provided from Cape Town water sources.
The source says it is possible water consumers have become more sensitive to the taste or odour of Geosmin, while in the past it was generally only detected when 20 micrograms were present per liter.
They continued that the compound can be treated with powdered activated carbon to absorb it. Most treatment plants are not set up for this so they have had to be innovative to treat water.
However, the source says treating the organic compound is not currently a primary concern, due to the fact that it is harmless if consumed.
Kalebaila said, “Geosmin can be removed from raw water using adsorption processes, for example with activated carbon. Biologically active sand filters (biological filtration) can also be used.”
Worsening drought conditions may also affect Geosmin levels.
“Cyanobacteria are found in nutrient rich water bodies. Drought conditions have an influence on the water volume, and will result in reduced dam levels, and as such the levels of Geosmin will be higher because of the concentration factor.”
A month ago, an employee of the department of engineering involved with water services at Stellenbosch Municipality said: “We have South African National Bureau of Standards codes that we must adhere to and all the water we produce must fall within the limits of the Bureau standards”.
This was in response to public concern that drought conditions could result in a poorer quality of water and water treatment. “We monitor all the water through the treatment process and the final product and we also monitor the water in the networks,” he said.