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Teralitre – terribly large number


Total storage capacity of all the public dams in the Western Cape adds up to 890,000 megalitres.  That big number is almost 1 teralitre.  As of October 17th, the amount of water stored in the same dams was 0.56 teralitres - roughly 62% full.  For the Cape in April, this would be a comfortable position.  Nearing the end of October, the picture is slightly different.  The rains are pretty well over.

The estimated population of greater Cape Town is 3.7 million.  Assuming each person uses 100 litres per day for eating and hygiene purposes, the volume of water required to sustain that same population for one year is 0.14 teralitres.  Comparing this demand to the available resource, it seems that we are home and dandy.  The dams have 0.56 teralitres - enough water to last 4 years.

However, the 100 litre per person per day allowance does not include water used for irrigation, water used by industry and agriculture.

Adding to the head-ache of our suffering city fathers is the state of the dams.  As the levels drop, the ambient water temperatures start to rise.  This can adversely effect water quality.  Biological activity climbs with increase in temperature.  Dissolved oxygen is inversely linked to temperature, thus a warm body of water will hold proportionately less dissolved oxygen.  Depleted oxygen levels are not great for fish, but boom times for anaerobic bacteria.  Decomposition processes speed up with concomitant rise in gas production and an increase in pH.  All the charm of a stagnant pond.


The City is considering implementation of Level 3 water restrictions effective from November 1st.  Water pressure will also be reduced in some areas to assist in the water saving drive.  For water consumers, options include

Boreholes and well-points are options for some.  In times of drought, these too will be effected.

A teralitre is a wonderful buffer if in the black, a disaster if in the red.

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