RAINWATER HARVESTING IS KEY WEAPON IN FIGHT AGAINST CLIMATE CHANGE by Gerry Quinn, product manager for Klargester's Envireau rainwater harvesting systems

As droughts and other climactic problems are expected to become more commonplace in future, water conservation and reuse are becoming increasingly important issues for the UK construction industry.

In addition to using treated drinking water more sparingly, we need to look to other sources for many of our everyday needs if we are to combat some of the effects of climate change.

Rainwater harvesting is an ideal solution since rainwater can be safely used for a variety of non-potable purposes in and around a home or business, including flushing toilets, running washing machines and cleaning vehicles and equipment.

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 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. However, they are ideal for new-build properties, where the cost of plumbing them in is often negligible.

We have recently 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.

It pumps water direct to an outside tap or garden sprinkler and, since it does not require any internal plumbing, it can be easily retrofitted. Tanks are available in the following sizes - 2,800, 3,800 and 4,600 litres.

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 about nine years ago and are currently used in about one per cent of new developments. However, this figure is expected to rapidly increase in future as the effects of climate change force us to re-evaluate the way we use our water supplies.

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