RAINWATER HARVESTING COULD HELP TO PROVIDE A SOLUTION TO WATER SHORTAGE by Gerry Quinn, product manager for Klargester's Envireau rainwater harvesting systems

The summer of 2006 heatwave and ongoing water shortage in the South East of England provide sobering evidence of the way in which the UK climate is changing as a result of global warming.

As the effects of global warming continue to manifest themselves, the water crisis is expected to deepen. Already, we are witnessing a trend for short, sharp bursts of rain that cause soil erosion and flooding, and do little to fill underground aquifers.

In addition to using water more carefully, we need to find alternatives to using treated drinking water for many of our everyday needs in the future.

Harvesting rainwater is an ideal solution since rainwater can be safely used for a variety of non-potable purposes in and around the home, including flushing toilets, running washing machines, cleaning cars and watering the garden.

In fact, studies show that 55 per cent of domestic treated water could be substituted for rainwater, while 85 per cent of water used for commerce and industry does not need to be of drinking standard.

All rainwater harvesting systems operate using typical roof drainage layouts. This means rainwater runs down the roof and into the guttering and down pipes in the normal way before passing through a filter, which removes the leaves and debris. The rainwater is then stored in an underground tank containing a pump and filter.

Klargester manufactures two types of full domestic and commercial rainwater harvesting systems under the Envireau brand. The Envireau gravity system pumps water to a dedicated header tank in the loft space via an inline filter, which further cleanses the water. One of the great advantages of this system is that the header tank also has a mains water supply, so if the pump was unable to work due to a power cut, or the underground tank became empty, the system would automatically switch to mains water.

We also manufacture a direct system, which pumps rainwater direct from the underground tank to the appropriate household appliance.

The above systems are not usually retro-fitted to existing properties because of the extensive internal plumbing work required.

We have just launched a new rainwater harvesting system which is designed for use in the garden and could prove invaluable for people beset by hosepipe bans, or on water meters.

Known as Raintrap, the product is available in three different capacity sizes, with the smallest storage tank - 2,800ltrs - able to hold as much water as 560 average sized garden watering cans.

The Raintrap operates in the same way as the other Envireau systems. However, since it pumps water to an outside tap or garden sprinkler, it does not require any internal plumbing and so can be easily retrofitted. Tanks are available in the following sizes - 2,800, 3,800 and 4,600 litres.

Raintrap has many advantages over traditional garden water butts. In addition to being able to store far larger quantities of water, it removes the need to carry water around and does not flood when full, since the excess water exits via a soakaway.

Rainwater harvesting systems cost between £1,000 and £2,600, depending on the size of the system and specific requirements. However, this cost can easily be recouped in terms of money saved for people on water meters. For example, a full rainwater recycling tank for a two-storey house with a 100m² roof could provide enough water for 200 toilet flushes, 30 full washing machine cycles and 12 car washes. A 100m² roof area can yield up to 120m³ of rainwater per year with a value of up to £2.56m³, giving an annual saving of £256 for a property on a water meter.

Another key advantage is that when the rainwater has been used, it passes through the foul system, rather than the storm drains, meaning that it poses no flood risk. Consequently, rainwater harvesting systems are becoming a necessity for gaining planning permission in some areas of the UK that could be at risk of flooding, particularly where regulators insist that surface run-off must be no greater than if the land was used for agricultural purposes.

Rainwater harvesting systems were introduced to the UK only about eight years ago, but they have long been popular abroad. For example, they have been used for about 20 years in Germany, which does not have as much rainfall as the UK and is more reliant on groundwater.

They are currently used in about one per cent of new developments in the UK, although this figure is expected to rapidly increase in the future.

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