Calculating the cost of water leaks in Johannesburg: How we did it

20 Sep 2016

Ujuh CorrespondentĀ 

On observing the massive water leakage on a north-eastern suburb of Johannesburg we sort to quickly calculate the wastage rate given the fact that the city is suffering from severe drought conditions.

The leakage on the corner of Lords and Beatrice, in Windsor East, Ranburg, ran for more than more than 36 hours. We calculated the damaged pipe on the corner of Beatrice and Lords was spilling water at an approximate rate of 27 000 litres per hour. In 36 hours, about 723 600 litres of clean water was wasted. This amount of water is enough to cater for the monthly water needs of about 25 households.

Being lay persons we employed rudimentary techniques to capture the run rate of the water leakage. Was our technique appropriate? We leave it up to you to judge and correct us if you will.

The leak on the corner of Lords and Beatrice was at source spilling onto opposite directions. One body of water was running down Lords Avenue and another was running down Beatrice and turning into Viscounts Avenue. The run rate was more or less equal to the naked eye. And there was another smaller leak down Lords Avenue which seemed to be connected to the bigger leak at the corner of Lords and Beatrice. This meant that there were two bodies of water running down Lords Avenue on both sides of the street edges.

How did we measure the water run rate?

We conducted our calculation on Lords Avenue where there were two leakages running on both edges of the tarmac. The bigger water run covered a surface of about 1 metre and the smaller one about half a metre.

Armed with an iPhone and a 9 litre bucket we went to work, starting with the bigger water run.

The idea was to capture the rate at which the water was running through a certain point.

Our starting point was to employ the bucket and the iPhone to show us the rate at which the water was filling up the nine litre container. Trouble is, we were not going to find an angle that will actually fill the 9 litre container at one go. To do that you needed to have the bucket positioned at a 90 degree angle to the surface. You would have to dig a hole onto the ground to get that angle.

So we resolved to have the bucket on a 180 degrees angle to the surface of the running water. At that angle you will have to let the water run into the bucket and lift it up just before the water bounces back from the bucket to escape. You would have captured water that fills only one quarter of the bucket.

And so we captured the rate at which the water was running into the bucket to occupy a quarter of the bucket. Using the stop watch on the iPhone and the 180 degrees water capturing angle, we saw that it took about three seconds for the water to fill quarter of the bucket. And so we multiplied this rate by four to arrive at the rate at which water run rate will fill the 9 litre bucket. And so we arrived at a resolution that the water was filling the 9 litre bucket in 12 seconds.

But there was a gap still on our calculation. A bucket positioned on a 90 degrees to capture a run rate of water that is covering 1 metre of the surface leaves a significant amount of water running on peripherial sides of the bucket. To account for the uncaptured water, we multiplied by three the amount of water running into the 9 litre bucket per 12 seconds. And so we arrived at a run rate of 27 litres per 12 seconds.

Remember that there were two leaks on Lords Avenue. We had just captured the run rate in the bigger body of water. And so we repeated the technique on the smaller body and arrived at 13 litres per 12 seconds.

Also remember that the damaged pipe on the corner of Beatrice and Lords was spilling into opposite directions, down Lords and Viscounts. And we had noted that the bodies of water running down both into Viscounts Avenue and into Lords Avenue looked equal to the naked eye. As such we imposed the Lords Avenue run rate onto Viscounts.

From the three water runs, we arrived at a figure of 67 litres per 12 seconds second. This then adds up to 335 litres per minute and 20 100 litres per hour. In 36 hours this leakage has wasting about 723 600 litres of clean water.

This opiece was lifted from our sister publication

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