The Advantages of Rainwater Harvesting Over Other Sustainable Options

Published: 28th April 2010
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Sustainable options, green options and renewables - the pressure is on us to do each one of these, and we know we should. However, it all seems so difficult and it is expensive and the return on the investment could be so long. We might not even be alive to see the benefit.

Rainwater harvesting is one of these options and is something we can all understand quite easily. After all, our ancestors were doing it for centuries until mains water arrived, and it is not rocket science. Generally people with gardens have one or two water butts. Rainwater harvesting is just using water butts on a much larger scale and using rainwater for far more than just watering the garden. Fifty percent of the 150 litres of water we use daily does not have to be mains water, that is to say, drinking quality. 30% literally goes down the toilet.

By collecting rainwater from our own roofs we could do without half of our mains water needs by using rainwater for all outdoor use, WCs and washing machine. However, if this is to be done effectively, we must allow for a storage tank that is much bigger than our normal 200 litre garden water butt. An average home needs a tank that, depending on the area rainfall and domestic needs, could range from 2000 to over 6000 litres.

Rainwater is best stored underground to keep it fresh and cool, so the hole required, for example, would be 3 metres deep and 2 metres wide. The rainwater is filtered before entering the tank, and then pumped to where it is needed. Rainwater harvesting kits which include everything needed for an average home cost between ?2000 to ?3000. As with all sustainable options, installation is best done in the context of a new-build or major renovation where installation costs get swallowed up in the overall works. Retrofitting costs centre on digging the hole and altering plumbing to provide a separate supply system to the WCs and washing machine.

Seen purely in pay-back terms, the investment could take 5 to 10 years to recoup and is achieved by lower water bills. Maintenance costs are low.

How do other green options compare with rainwater harvesting?

Solar water heating via panels on the roof has been around for several years. You will need 4 to 5 m2 of ideally south facing roof area for the panels. The system works all year round, though water will need to be further heated with a boiler or immersion heater during the winter months. If a dedicated solar cylinder is not already installed then you will need to replace the existing cylinder, or add a dedicated cylinder with a solar heating coil. Most conventional boiler and hot water cylinder systems are compatible with solar water heating. A solar hot water system may not be compatible if the existing boiler is a combination (combi) boiler and there is no hot water tank.

Costs for a typical solar water heating system range from ?3,000 to ?5,000. Hot water heating bills can be reduced by a quarter to a third and the payback period can be less than 10 years. This is dependant on which fuel you are replacing (an electricity saving will pay back sooner than gas or oil).


Rainwater Harvesting Limited supplies rain water harvesting storage tanks, pumps, filters and management systems to households and commercial businesses. is a large information resource offering valuable technical information and advice in addition to 1000s of product specifications. Download the invaluable rainwater harvesting tank size calculator

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