Rainwater Harvesting




Much of the water we use doesn't need to be of drinking quality. At home and at work, we flush toilets, wash vehicles, launder clothes and water gardens with nothing less than drinking water!

In fact, studies show that 55% of domestic treated water could be substituted for rainwater, while 85% of water used for commerce and industry does not need to be of drinking standard. As global warming disrupts weather patterns, causing drought and flooding by turns across the country, Codes and guidance have been introduced to ensure we manage our water better.

Architects and builders are now routinely building in systems to ensure we conserve water stocks. And some of the systems most frequently installed at the moment are those designed for rainwater harvesting. In simple terms, these are designed to capture and store rainwater that falls on the roof for reuse in the home and in businesses.

They are now becoming a necessity for gaining planning permission in some areas of the UK that could be at risk of flooding, or where the mains water simply cannot support demand and requires back up. What follows is an introduction to rainwater harvesting, the cost-savings that can be achieved with a system and how in future you will be able to know that your system is fit for purpose.


How they work

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.

The water can be used, with or without the addition of a header tank, for a variety of non-potable uses including flushing toilets, washing vehicles, gardening and washing clothes.

However, this type of system is not usually fitted to existing properties because of the extensive internal plumbing work required. They are more suited for new-build, where the cost of plumbing them in is often negligible.


Garden usage

A more typical ‘retro-fit’ rainwater harvesting system on the market at the moment would be one designed for watering the garden. The garden can consume up to 50% of peak demand in the summer, so keen gardeners that harvest rainwater could save thousands of litres of tap water each year, as well as cutting bills and energy usage.

For example, the Kingspan Raintrap system collects, filters and stores the rainwater in a large water storage tank. The water is then pumped under pressure from the tank to a hose or sprinkler, which means gardeners no longer have to trudge back and forth to the water butt, filling and refilling a watering can. And, as an added bonus, plants will thrive on the warm, soft, chlorine-free rainwater. It can easily be installed by the property owner because no internal plumbing work is required.


Cost savings

Rainwater harvesting can not only help conserve water supplies, it can also bring significant cost savings for properties on water meters.

A full rainwater recycling tank for a two-storey house with a 100m² roof can provide enough water for 200 toilet flushes, 30 full washing machine cycles and 12 car washes and give an annual saving of £256 for a property on a water meter.


Standards/Consumer Confidence

As with all new technology, there needs to be standards set down to ensure that all the systems that are on the market are fit-for-purpose. Kingspan Water’s Technical Director, Mike Norton, who is also chair of the UK rainwater harvesting association, has been at the forefront of ensuring measures are now in place.

The British Standard for rainwater harvesting, BS8515 which provides expected criteria for rainwater harvesting equipment manufactured in this country has just been published. BS8515 aims to ensure comfort for you, and compliance by suppliers, to minimum standards. It also addresses any concerns about the possibility of cross-contamination of mains drinking water with rainwater.

Meanwhile, Mike has also helped to ensure that any concerns about the quality and purity of greywater will be alleviated by the new British Standard BS8525 for greywater will be introduced later in 2009.

And he is at the forefront of a call for a national training programme that will ensure standards of installation are meeting minimum criteria.


In summary

To conclude, rainwater harvesting provides a viable means of conserving water supplies and making the best use of a natural resource that we simply can no longer afford to throw down the drain.


Written by: Andy Thompson, KingspanWater’s Divisional Market Development Manager

For further information, call Kingspan on +44 (0) 1296 633139, or visit their website www.kingspanwater.com.