Harvesting rainwater

Rainwater harvesting is the collection, storage and distribution of rainwater. The perfect storage facility is a water tank. Rainwater can essentially be used anywhere where tap water is used. The idea of using drinking water to flush toilets and water lawns is wasteful especially in light of the population growth and current water shortages across the country.

Rainwater can be used for all household purposes, including irrigation, refilling pools, flushing toilets and washing cars.

The most efficient roof surface for rainwater harvesting is a metal roof. This means a corrugated iron, flat iron sheet or IBR profile. Tiled roofs are not as efficient for collecting rainwater, and you cannot harvest rainwater from a thatched roof.

HOW IT WORKS

Water rain runners are fixed to each of the gutter downpipes to initially harvest the rainwater. This water is fed into rainwater storage tanks, and a pump system is used to pump this water from the rainwater tanks to the house.

AVERAGE CALCULATIONS

Metal roofs: 11mm of rainfall produces 1 000 litres of harvested rainwater for every 100m 2 of roof area. Tiled roofs: 16mm of rainfall produces 1 000 litres of harvested rainwater for every 100m 2 of roof area.

STORAGE TANKS

Tank sizes for rainwater storage include 1 500 litres, 2 500 litres and 5 000 litres. Although 10 000 litre water tanks units are available, this size is very unwieldy.

When considering the size of water tanks, these factors should be taken into consideration:

• How many people are there in the house? The more people using water, the less rainwater storage is needed and vice versa

• What is the size of roof area? The greater the area that is harvested, the greater storage capacity can be viably installed

• What type of roof do you have? The more efficient the surface, the more water can be harvested

• What is the rainfall pattern? How much and how often does it rain?

WHERE TO PLACE THE TANK

Water tanks no longer need to stand at a wall under the roof eaves. It is possible to fill a rainwater tank or multiple rainwater tanks without the need for any pumping. Simply make use of gravity to make rainwater harvesting sustainable.

WATER RUNNER SYSTEM

A water runner system will deliver water to any place around a house or garden so long as the head of the water runner system is higher than the head of the tank.

The water runner system is a self-cleaning device placed in your downpipe to send harvested rainwater in an underground pipe to water tanks without any chance of the delivery pipe blocking or clogging in any way. The system receives the water, sieves out any debris and delivers the water via an underground pipe to the remote water tank.

Water pressure for household use:

A pump to pressurise the water for the supply is used to deliver water. The pump starts soon after a tap is turned on and switches off after all taps are closed. This is automatic.

The whole system involves:

• Installing a system to harvest rainwater into each downpipe

• Installation of suitable size and number of rainwater tanks

• A pump to deliver the water to the house. If there is a need for high peak times of water usage, more pumps can be installed in parallel to increase the higher volumes required

• Electrical supply point

• A ball valve to augment supply in the water tanks from municipal mains. This gives an emergency supply at all times

• An override to revert to municipal mains should the rainwater be exhausted.

RAINWATER TANK TIPS

• Install gutter mesh to prevent leaves and debris from blocking gutters

• Fit enough gutter outlets on the underside of the gutter to prevent obstruction of water flow

• A ‘Leaf Eater’ can be installed onto downpipes. This is a simple and effective way to prevent blockages

• Install a tank screen at the tank entry point to filter water and keep mosquitoes and pests out

• Consider annual rainfall, roof catchment area and water usage when determining the size of the tank you want to install

• Use a tank top up system (if required) to automatically top up the tank with mains water when water levels fall to a designated minimum level

• Select a pump system (if required) to distribute water for use inside or outside the home. On simple systems, gravity will do the trick too.