Harvest rainwater and reuse household water – then get your own wetland going
By harvesting rainwater and reusing household water, you can reduce your water bill and become a steward of this precious resource and not just a consumer. Beverley Ballard-Tremeer explains.
South Africa’s average annual rainfall, 464mm, is about half the world average. Add this statistic to the water needs of our fast-growing population, and potable water is bound to become an expensive luxury in the future. Water is a precious resource, not to be used wastefully and certainly not to be thrown away. Yet we do exactly that if we don’t make the most of rainwater and grey water.
Seasonal rains can be a great benefit to plants. A rainfall of 10mm will produce about 500ℓ (or 0,5kl) from 100m2 of roofing, and a property of 4 000m2 will produce 20kl! The average homeowner could collect tens of thousands of litres of rainwater each year if they set about harvesting it. Imagine the saving on your water bill!
Harvesting rainwater works well in regions that have heavy rainfall or prolonged rainy periods, both of which result in run-off. Along with water-wise gardening techniques, rainwater can provide much of the water needed by your plot. If you have sufficient storage tanks, harvesting water during peak rainfall seasons ensures water will be available during drought or when water restrictions are in effect. Making use of rainwater also reduces reliance on underground wells, pumps and municipal water systems. Moreover, rainwater is free and clean.
Farmers and smallholders have long known how to capture the rain that falls on their properties, for example, by constructing dams and furrows, and installing water tanks. How to conserve water in the home and garden is now becoming common knowledge for all homeowners, and new technologies are being developed all the time. These days, a wide range of durable water tanks that can be attached to gutters are available to capture rainwater run-off from the roof. Some property owners in the platteland are familiar with using household grey water for landscaping, and now several golf estates, hotels and commercial properties in South Africa are doing the same. Age-old techniques of preventing rainwater run-off on sloping sites are also being re-examined. >
on the amount of run-off) and plant a border, vegetable garden or orchard. The same can be done to capture runoff from a neighbouring property. • Wetland, pond or bog garden The lowest part of a sloping property is ideal for these types of features. Use French drains with piping, or berms and swales, to direct run-off here.
Harvest rainwater from your roof
Collecting rainwater from the roof is the most efficient means of harvesting. To find out how many litres of water you can harvest from your roof per year, using the national average annual rainfall of 464mm as a baseline, multiply the roof area (or the area of your house) in square metres by 515,5ℓ. Divide by 1 000 to get the number of kilolitres. Deduct this amount from your annual water bill to see how much you will save for the year. If your annual rainfall is higher, the savings will be greater, and vice versa.
Rather than letting this free water run off your property, use it by directing the water to where you want it or by storing it in water tanks for later use in the garden. Which of these choices best suits you depends on your budget, your landscape and whether there is a slight slope away from the downpipes.
• Redirect roof rainwater run-off
The downpipes from gutters can be connected to or feed into surface-laid flexible tubing or pipes, underground piping (for example, a Flo-Pipe) or a French drain to redirect water into particular areas. Or let the water from the gutter be channelled along a dry stream bed lined with strong plastic sheeting topped with pebbles. Even a shallow channel across a lawn can serve to direct run-off to a border, >
a vegetable garden, an orchard or a pond.
A slight slope downwards from the downpipe is necessary. This method works particularly well if the areas where the water is directed are somewhat sunken, so that sufficient water collects there to wet the soil thoroughly. The trendy name for such an area is a rain garden. If the water is used in a pond for wildlife, a simple filter may be needed, as bird droppings and pollutants may wash off the roof.
• Save roof rainwater in a tank
If redirecting water is not practical, invest in a water tank for rainwater storage. A tank is usually positioned at ground level, but if you’re in the process of building a house it is possible to bury your tank underground. Tank-stored rainwater can be used in the home for bathing and showering, as well as in the garden – although this would involve professional plumbing alterations and additional filtering accessories. City rainwater is not recommended for use as drinking water.
Rainwater tanks are available in durable polyethylene plastic in a range of sizes, and in colours that blend well with a variety of home exterior finishes. Traditionally, water tanks have been cylindrical with a large diameter. Nowadays, slimline tanks are available that are ideal for small urban properties. Their 750mm diameter means that they can be positioned in an alleyway or next to the garage. The slimline tanks come in various sizes, the largest holding 2 000ℓ. Any number of tanks can be joined together against a wall in order to maximise your water harvest. The smaller tanks, which are only 1,8m high, could even be used in townhouse complexes with shared internal walls, as they would fit through internal doorways. Rectangular tanks are also available.
Pumps, level gauges, leaf traps, first-flush diverters that divert the initial “dirty” roof rainwater, as well as taps, valves and other fittings to help connect your tank to your pumps and irrigation systems are all on offer.
Water tanks must be placed on a completely level base so they don’t subside. Properly laid precast concrete pavers and brick paving are able to support the smaller tanks. Alternatively, place them on a 75mmthick concrete base or find a metal tank stand.
• Rainwater tanks are easy to install
Decide where you want to position the tank or tanks. Then cut a hole in the gutter above the tank position and in the lid of the tank, using a circular cutter available from hardware stores. Insert the downpipe and seal the joins with silicone.
TOP Terraced areas help to hold run-off on a sloping site. MIDDLE Construct paths and driveways with the centre or one side slightly raised to direct run-off into adjacent borders. BOTTOM A slight swale in a lawn directs run-off from a paved area to a border.
Run-off from a gutter can be directed into a curving dry stream bed containing irregular-sized rocks to help slow the flow. If you want to direct the water to a pond, line the bed of the stream with strong plastic sheeting topped with pebbles.
With sufficient storage tanks, harvesting water from the roof during the rainy season ensures water will be available during dry periods or when water restrictions are in effect.