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LOCAL TIME: 10:15 pm | Tuesday, 29 September
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Install Water Tanks to Harvest Rainfall

Categories: Green Living, Homes and Gardens


Capture Rainwater from house gutters.



 Two 750-litre tanks side-by-side on a cement plinth. Connected to down point on the house gutters.


The system?


Short length of 75mm piping connects the tanks to the gutter. It collects water from a roof area estimated at 90 sqM.



Interconnection of the new pipe routing rainwater to the tanks instead of, as before, into the downpipe to the drains.



Rain water is routed down through a hole cut in the removable lid of the first tank. There is a removable filter under that lid to catch leaves and other loose materials flowing down off the roof; it can be cleaned from time to time.



Water flows between the two tanks through the open blue pipe to balance levels. Any dirt should tend to collect at the bottom of the first tank. So content of first tank can be used for irrigation, while content of second tank is used for clean water.




In case of heavy rains, the white pipe routes surplus overflow from the top of the second tank down to the drain. Each tank has a simple valve with a quick fit outlet for snap-on hose fittings. Dirtier water from the first tank can go to the garden and cleaner water from the second tank used for inside use.

Likely Outcome?

davIt is estimated that during a rain shower, approximately 0.65-0.85 litre of water can be captured for every 1 square metre of roof area being drained. So, given that an average shower is 15-20mm of rain, it is expected that this system, connected to 90 sq.M of roof, will harvest and store sufficient water to fill both tanks; i.e. about 1500 litres.

The system can be extended by adding another two or three tanks in line, while the area of roof drained to the tanks can also be doubled.


Seeing one can with effort reduce consumption for personal use 25 litres per person per day then in a crisis of water shortages these two tanks could provide two of us with enough water for a whole month. With addition of 2 more tanks this system could provide water for another 2 people for one month.

Mission accomplished: after three bouts of 5-10mm rain both tanks are filled to the top and ready for use. The system is working precisely as planned.

From the rainfall table below it can be seen that the average rainfall in Cape Town (where this house is) is such that it is only in the Feb/Mar period that one may run short.


At other times, when normal water supplies flow through the municipal system, then the rain water harvested by this system can also be used for irrigation and other cleaning purposes, thereby reducing the amount of fresh drinking water used while lowering overall water and sanitation costs - achieving lasting security of water supply and economy of water use.