How to harvest rainwater and cut your water bill

11 Jan 2017

What is rainwater harvesting? 

Stored rainwater can be used in the garden. It can also be used for topping up ponds and swimming pools, car washing and hosing down paved areas, and as drinking water for livestock and pets.
According to William Heslop from Baobab Water Solutions, rainwater harvesting is simply the collection, filtering and storage of rainwater for reuse on site, rather than allowing it to run off. 

He says the rainwater is usually collected from rooftops but can also be collected from other types of man-made above ground hard surfaces.

How does rainwater harvesting work?

William says water is diverted from the downpipes and off the roof into a rainwater tank or tanks.

Usually, a leaf guard or first flush filter is installed on the downpipe to filter the water before it goes into the tank. The water is then stored in the tank until required, he says.

A pump is installed near the tank to provide pressure to run the water from the tank to where it is required. William says if the water is to be used in the garden or swimming pool, and the gradient of the property is sufficient, it may not be necessary to install a pump.

What can the water be used for?

Stored rainwater can be used in the garden, says William. It can also be used for topping up ponds and swimming pools, car washing and hosing down paved areas, and as drinking water for livestock and pets.

A system with several collection points, a 5 000 litre JoJo tank and a 0.37kw pump with pressure control and cover are in the region of R17 000.
He says it can also be pumped into the house, but the water will require treatment to ensure it is of potable standard. This requires a more complex and costly system.

Approximately how much can homeowners expect to pay for a rainwater system?

William says the cost of the systems vary greatly depending on the size and number of tanks required, and the layout of the site. As a general idea, he says systems start at about R10 000 for a simple system using a 2 500 litre JoJo (or similar) tank and gravity feed to the garden.

He says a system with several collection points, a 5 000 litre JoJo tank and a 0.37kw pump with pressure control and cover are in the region of R17 000.

How much water can a rainwater harvesting system save?

From 1mm of rain, homeowners can harvest 1 litre of water per 1sqm of roof.

William says potentially this means that an annual rainfall of 500mm on a roof surface of 50sqm can harvest up to 25 000 litres of water. He says the number and size of tanks required would depend on your roof size and structure, and the space available for the tanks.

What should homeowners look for in a rainwater harvesting system?

The biggest problem with rainwater harvesting is storage space. One could potentially collect more water than the available storage. To make the most of your system, install the biggest tank your budget and space will allow.
The biggest problem with rainwater harvesting is storage space, says William. He says one could potentially collect more water than the available storage. To make the most of your system, install the biggest tank your budget and space will allow.

The house needs to have gutters to channel the water from the roof to the downpipes. The tank, however, doesn’t need to stand against the house - it can be positioned in the garden as long as the top of the tank is lower than the roof where the water leaves.

William says the tank should be correctly installed on a firm and level surface, preferably on a concrete base. Overflow pipes should be attached to the tank to redirect any overflow to a suitable area of the garden.

A properly installed system should filter leaves and other debris before they get into the tank.

How can homeowners maintain their rainwater harvesting system?

To keep your rainwater harvesting system in tip-top condition, keep the gutters clean, cut back overhanging branches from the roof, and check that the leaf guard or filters are clear and not blocked.

To save water, homeowners should cover swimming pools when not in use and check for water leaks and dripping taps.
William says if there is a tank screen on the tank, ensure that it is emptied regularly.

How can homeowners save water?

William says homeowners should be aware of water usage at all times, even during the rainy season and even if you have a rainwater tank or borehole.

Water is a non-renewable resource - it cannot be manufactured, and we live in a water scarce country. Check for water leaks and dripping taps and don’t water your garden in the middle of the day. William says early mornings or evenings are the best time to cut down on evaporation.

He says a layer of organic mulch will slow water run-off and evaporation, and it discourages weeds which compete for water. To save water, homeowners should cover swimming pools when not in use, he says.