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How to install a rainwater harvesting system


Cape Town and Johannesburg residents are facing stringent water restrictions following the protracted drought. This helps to remind us all that water is vital to life and is such a precious natural resource that it makes sense to collect every drop of rain and recycle grey water and back-washed pool water. In fact you can reduce your water bill by as much as 90% by harvesting rainwater and grey water.

How to install a rainwater harvest systemwater-on-roof

  • The tank should be placed on a solid flat, level surface.
  • Your house must have gutters and accessible down-pipes.
  • Several down-pipes can be directed to one tank.
  • A leaf catcher or first flush filter should be installed on each down-pipe.
  • Generally a pump will be needed to pump the water from the tank into the garden, so you’ll need accessible electricity.

The rainwater tank doesn’t have to be placed next to your house, and can go anywhere in your garden or be buried underground as long as the top of the tank is below the level of the filter or leaf catcher.

Rainwater tanks are quite large: A standard 5,000l tank is about 2.2m high and 1.8m in diameter. The biggest disadvantage of rainwater harvesting systems is a lack of storage capacity, so it’s best to buy the biggest tank that space and budget allow. The simplest way to calculate the size of the tank you will need is by taking a look at the size of your roof. Generally a 50m² to 100m² roof = 750l to 2,200l tank, and a 200m² to 400m² roof = 2,500l to 10,000l tank.

We are all becoming increasingly aware of the importance of water to our survival as well as the decline in water quality and reliability of supply. Water conservation needs to be a way of life. If we all try and save water we can make a huge difference to the environment.

What is rainwater harvesting?

A well in Burano, an island in the Venetian Lagoon, northern Italy

A well in Burano, an island in the Venetian Lagoon, northern Italy

Rainwater harvesting is the collection, filtering and storage of rainwater for reuse on site. It’s usually collected from roof tops and can be used in the garden, for car washing and for drinking water with proper treatment. Collection of rainwater can help mitigate flooding of low-lying areas and reduces demand on wells which may enable ground water levels to be restored. In addition, rainwater harvesting in urban areas reduces the need for clean water in water distribution systems and less generated storm water in sewerage systems as well as a reduction in storm water runoff polluting rivers and lakes.

Why a landscaper would not use grey water continually to irrigate his plants

Rainwater harvesting is not new – around the 3rd Century BC farming communities in Balochistan (now located in Pakistan, Afghanistan and Iran) used rainwater harvesting for irrigating crops. Not many people know that Venice depended on rainwater harvesting for centuries as the lagoon that surrounds Venice is brackish and so not suitable for drinking.

Who is Claire Cardwell?

Claire Cardwell of Blue Designs is an architectural designer with over 15 years experience in the Johannesburg area. She has worked on small projects – double garages, swimming pools – and new houses from a 1,300m² house in Featherbrooke Estate, to houses of only 110m² in size. In 2015/2016 she worked on a small complex, a warehouse, a nursery school and new houses in the Waterfall Country Estate, Copperleaf Estate, and in Limpopo on an old-age home and frail care facility in North Riding.


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