Bad-tasting water not toxic

2019-02-06 06:00

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The recent bad odour and unpleasant taste of water in the Mangaung Metro Municipality is due to algae.

This is according to findings by the University of the Free State’s (UFS) experts on water affairs. They are Dr Tascha Vos, water quality specialist, and Marinda Avenant, lecturer, both at the Centre for Environmental Management at the UFS.

While the quality of water remains a concern for consumers, the water is not toxic, according to the experts.

“Algae, which are naturally present in raw water, can produce organic compounds, such as geosmin and MIB, which give the water this earthy odour and taste,” said Vos.

“Even though humans are very sensitive to the taste of these compounds (some people can detect geosmin at concentrations as low as 10 ng/l), these compounds are non-toxic.

“It is not easy to remove the geosmin and MIB from water by conventional treatment methods. Methods such as biological activated carbon in filters, ceramic filters and ozone treatments, can be used to remove the taste.

“Geosmin and MIB are generally removed by means of evaporation when the water is used for cooking,” Vos explained.

“Some stores and general dealers do sell affordable activated carbon filters for water jugs or bottles. Algae are removed from the raw natural water by the conventional purification treatment methods used by water providers like Bloemwater and the Mangaung Municipality, and thus pose no serious health threat.”

Climate change and extreme hot weather conditions have been found to be among the contributing factors to the quality of drinking water.

“Algae are more abundant in the dams (from where water is abstracted for domestic use) in summer due to the higher water temperatures.

“Also, algal growth is stimulated by a higher concentration of nutrients in the rivers and dams during drier periods.”

Vos said findings made were that these compounds were also present in mushrooms and some vegetables such as beets, giving these their earthy taste.

Water sources and dams supplying the Greater Mangaung with water are under extreme pressure due to climate change. The pressure is due to, among other factors, drought.

Bloemfontein residents receive their potable water from two main sources, namely Bloemwater and the Mangaung Metro.

The southern parts of Mangaung (broadly the suburbs south of Nelson Mandela Drive) receive their water from Bloemwater.

Bloemwater extracts water from various sources to supply these areas:

  • Bloemfontein area: Welbedacht Dam (Caledon River)
  • Botshabelo and Thaba Nchu areas: Rustfontein Dam (Modder River), Groothoek Dam (Kgabanyane River)

The northern parts of Mangaung receive water from the municipality, which abstracts water at the Masels­poort Weir (Modder River).

Avenant said conserving water and managing the city’s water demand in order to provide consumers of the Mangaung Metro during times of drought remains a challenge.

“Bloemfontein is at a point where its water needs exceed its supply of bulk water and is pre­sently in a very unsustainable situation.

“Increased efforts to conserve water and manage the city’s water demand are urgently needed,” said Avenant.

An alternative effort to conserve water to supply Mangaung during dry periods is sourcing water from the neighbouring Lesotho.

“During dry periods, the water in the Welbedacht Dam can be supplemented with water from the Katse Dam (Lesotho), as they are currently doing.

“The water in the Modder River (Rustfontein Dam and Maselspoort Weir) are supplemented with water that are pumped from the Caledon River to Knellpoort Dam (in a tributary of Caledon River), and then pumped via the Novo pump station to the upper reaches of the Modder River near Dewetsdorp.”

Avenant said the municipality, as part of a longer-term strategy, was investigating the possibility of transferring water from the Gariep Dam via a buried water pipeline of close to 180 km.

“This pipeline could also provide some water to some of the smaller towns in the southern Free State situated within reach of the pipeline,” Avenant said.

Algae, which are naturally present in raw water, can produce organic compounds, which give the water this earthy odour and taste – Dr Tascha Vos


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