Harvesting Rainwater


Did you know that by harvesting the rainwater that falls on your property and reusing household water you can collect sufficient free water to meet the water requirements of your garden? The rainfall that falls on the roof of a house can be harvested to provide most of the water needs of a well planned water wise garden. If you select low water usage plants for a small garden rain water harvested from the roof will provide sufficient water for the garden. South Africa is a water-short country and water needs to be conserved. We have an average annual rainfall that is less than half of the world’s annual average rainfall. As more demands are made on existing water supplies by an increasing population and increasing commercial and

residential development, it is inevitable that a time will come when our demand for water will outstrip supply. Clearly water is a precious resource, not to be used wastefully and certainly not to be thrown away. And yet we do, as it were, throw it away, by not making the most of the rainwater and ‘grey’ water available to us. We need to save every drop of rainwater that falls on our properties, whether residential or commercial – this is known as rainwater harvesting. We also need to seriously consider reusing our bathing and laundry water to water the garden – such water is known as ‘grey’ water. Municipal by-laws regulating the use of grey water vary, so homeowners are advised to contact their local authority to find out if there are any restrictions.

Harvest rainwater from the roof
Harvesting rainwater works well in regions which have heavy rainfall or prolonged rainy periods, both of which result in water run-off. If you utilise all the principles of water wise gardening, rainwater can provide nearly all the water needed by your garden. What a saving on your water bill! When the rainy season ends, and the rain tanks finally run empty, then grey water can be used to water areas such as lawns, trees and shrubs.

Water for free
Collecting rainwater from the roof is the most efficient means of harvesting water. Did you know that every 1m² of roof will generate 1 litre of water from 1mm of rainfall?
To find out how much rainwater in litres can be harvested from your roof per year multiply the area of your roof in m² (or the area of your house) by the amount of rainfall your area received per year in mm. Allow for 15% wastage. To change this figure to kilolitres, divide by 100. Rather than letting this free water run away from your property, use it by directing the water to where you want it, or by storing it in a water tank for later use in the garden.

Save rainwater in a tank
Invest in a water tank for rain water storage. A tank is usually positioned at ground level, but if you are in the process of building a house, it is possible to bury it underground. A pump will then be needed to bring water to where it is needed. Tank-stored rainwater can be used in the garden or in the home for baths and showers, although this will involve professional plumbing alterations and additional filtering accessories. Note that untreated rainwater is not recommended as drinking water.
Rainwater tanks are available in durable polyethylene plastic in a range of sizes, and in a variety of colours that blend well with various home exterior finishes, whether brick or paint.
Rainwater tanks are easy to install. However, it is vital that they are placed on a completely level base that will not subside. Properly laid precast concrete pavers and brick paving are able to support the smaller tanks. Alternatively, place them on a 75mm thick concrete base. Metal tank stands are also available.
Decide where you want the tank or tanks. Then cut a hole in the gutter above the tank