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 – such as plumbago, New Zealand flax, statice, pride of India and wild garlic – rainwater harvested from the roof will provide sufficient water for the garden.
A series of rectangular slimline tanks can be connected to provide storage for larger volumes of water. (Pic courtesy: Hydro Dynamics)
The new cylindrical slimline JoJo tanks come in variety of colours that will blend unobtrusively with any house exterior. (Pic courtesy: JoJo Tanks)
If there is a sufficient slope you can channel water from the downpipes of your gutters into a pond.
Rainwater can also be harvested from small roof surfaces such as outbuildings, roofed carports, garden sheds and Wendy houses.
National Water Week takes place during March, with the intention of raising awareness that South Africa is a water-short country, and that water needs to be conserved. South Africa has 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.
The Department of Water Affairs has predicted that the piped water needs of Gauteng and adjacent areas may exceed the available supply in three years’ time. Only in 2020, when the new Lesotho Highlands Water Project is predicted to start operating, will more water become available.
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.
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.
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? Put differently, if you receive South Africa’s average annual rainfall (464mm) you can harvest 464 litres (0.4 kilolitres) of free water per year per 1m² of roof – enough water for 2 showers.
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. Deduct this amount from your annual electricity bill to see how much you will save on water bills for the year.
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.
Connect the downpipes from your gutters to surface-laid flexible tubing or pipes, underground piping, a French drain, a dry stream or channel in the lawn planted with low growing ornamental grasses – such as mondo and liriope – to redirect water into particular areas of the garden. This may be the swimming pool, the veggie garden, fruit tree area, a nearby border, a wetland or pond in the garden. A slight slope downwards from the downpipe is necessary. A simple filter may be needed for water being used in a pond, as bird droppings and pollutants may wash off the roof.
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. Pumps, level gauges, leaf traps, first flush diverters that divert the initial ‘dirty’ roof rainwater, taps, valves and other fittings to help connect your tank to your pumps and irrigation systems are also available.
Traditionally, water tanks have been cylindrical with a large diameter. Now slimline tanks that are ideal for small urban properties are available. Their 750mm diameter means that they can be positioned in an alleyway or the side of a garage. There are various sizes of slimline tanks that hold from 750 to 2 000 litres of water. Any number can be joined together against a wall in order to harvest more water.
The smaller slimline tanks, with a height of only 1800mm, can even be used in townhouses with shared internal walls as they fit through internal doorways. Rectangular tanks are also available. Both cylindrical and rectangular can be joined in a series to form larger capacity tanks.
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 position, and in lid of the tank, or the first tank in a series. You can use a circular cutter available from hardware stores. Insert the downpipe and seal the joins with non-toxic, water resistant silicone.
Source: Life is a Garden (Beverley Ballard-Tremeer)
See a related post: Four Creative Ways to Harvest Rainwater for Gardening. Also read Benefits of Rainwater Harvesting Tanks in Urban Environments.
The JoJo 750 litre Slimline Tank is ideal for urban dwellers where space is a limitation and they can be connected-up in series for more rainwater storage capacity. If space and aesthetics are not an issue, JoJo Tanks have a wide variety of other water tanks suitable for rainwater harvesting and water storage.
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