South Africa: Clever thinking needed to deal with water supply issue

23 mars 2012

Creamer Media's Engineering News - March 23, 2012

I read a report in a local newspaper about South Africa’s water supply situation. The article contained a really dumb statement made by the journalist who wrote the article. He referred to water consumption and South Africa‘s ability to supply ‘this finite resource’.

Water is not a finite resource. Have you ever stood on the beach and looked at the ocean and wondered how you could drink all the water? I remember in school seeing a sign in a café that read: ‘Drink Canada Dry’. Well, you can’t. Water circulates around.

When you drink a couple of litres of water, a while later, your body returns the water to the greater system, mostly through the sewerage system. The water purification people then take that water and clean it . . . and then sell it to South African Breweries, which adds a few ingredients to it, bottle it and then sell it back to you.

The water that ends up on crops on farms also goes back to the greater system – either through the plant itself into the air as evaporated water or off the land directly as evaporated water or runoff. You cannot use up water.

The water molecule, H2O, is virtually indestructible. It is possible to ‘break’ a water molecule by electrolysis, but that requires a great deal of electricity being pushed into it. Then what you get is hydrogen and oxygen gas. The moment the highly inflammable hydrogen burns, it uses oxygen and turns back into oxidised hydrogen, which is nothing but water. So, all the water that existed on our planet at the time of the dinosaurs is still here.

In contrast to the journalist, Water and Environment Affairs Minister Edna Molewa said that, on current projections, South Africa‘s water supply could outstrip demand between 2025 and 2030. This is a reasonable statement. ‘Demand’ outstripping ‘supply’ does not mean that the water is ‘used up’. It means that much of the water ends up in a place where you don’t want it, like at the bottom of a hill, or in a sewage mixture.
Water supply is a cost and energy issue, not a water consumption issue.

When water has been ‘used’, it ends up at a lower point gravitationally speaking or it ends up dirty, as in sewage.
To reuse the water, you have to clean it and then pump it up to a high point so that it can run downhill to supply consumers.

It takes energy to clean and pump water. The energy system, in turn, means cost. We are fortunate that Mother Nature helps by lifting up some water by evaporation and then shifting it and dropping it as rain.

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Catégories: Eau

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