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Rainwater harvesting

How to save 50% on metered water costs


The UK practice of using mains water to supply all our water needs is needlessly wasteful, both financially and environmentally. Mains water is expensively purified to drinking water standards - but much of the water is used for non-potable purposes, like flushing toilets, cleaning and gardening. Harvested rainwater can be substituted for mains water, saving money and contributing to the protection of a key natural resource.

The idea of collecting rainwater has been around for thousands of years. Archaeologists have found that rainwater harvesting systems were being used in the Negev desert 4000 years ago. In Ancient Rome villas had their own individual cisterns and the rainwater was collected from paved courtyards which made them less reliant on the supply fed by the city’s aquaducts.

Today around the world rainwater harvesting is enjoying a renaissance and systems are being extensively installed for domestic, commercial and industrial use. In the UK the subject is being given a higher degree of priority now that mains water metering is becoming standard on newly built homes and for commercial and industrial applications.

In the home most people turn on a tap without any real thought of what is involved. The water is conveniently dispensed, and just minutes or split seconds later it disappears down the plug hole. It then embarks on a journey that may be several miles long before it can be cleaned and treated with chemicals before reappearing at the tap. This cycle is not only illogical but is polluting and wasteful.

Treated water is an expensive resource and so using free rainwater instead wherever possible makes sound ecological sense.

It is possible to collect 1700 litres of rain off a typical roof of 100 m² for every 25 mm of rainfall. For a typical 640 mm of rain a year in the South East and Midlands, 120 litres a day can be collected. In the wetter West and North, the same roof will give over 200 litres a day.

The Environment Agency estimates that the growth in water demand in the UK until 2011 will be the result of 20% from population growth, 40% due to increased consumption and 40% from leakages. But there are positive signs that the Government plans to attack the issue of conserving water resources.

In a recent consultation document, ‘Opportunities for Change’, readers are asked their views on whether there should be regulation to encourage water recycling in buildings. All the logic would suggest that the answer should be ‘Yes’! So installing rainwater systems ahead of regulation could save the extra expense in retro-fitting, keep water meter assessed bills to the minimum, and make an important contribution towards protecting the environment.

Rainwater is particularly useful to supply the large volume of water needed for flushing toilets. Each person on average uses almost 45 litres a day for this purpose. In an average household, this contaminates nearly 66,000 litres of drinking water a year. This is the main use of water in a household, closely followed by bathing and washing which uses 37 litres per person per day.

Rainwater is ideal for use in washing machines; on average people use 20 litres a day for washing clothes. The advantage is that the soft rainwater allows the use of natural soaps and biological washing powders, which are much more gentle on clothes than standard detergents. Not only this, there is less chance of skin irritation caused by detergents, and there is no environmental damage when discharged into the waste water system.

Gardeners through the centuries have recognised the importance of a plentiful supply of water, and that plants prefer natural rainwater instead of heavily treated mains water. A hosepipe uses a minimum of 500 litres an hour - almost as much as an average household uses in a day.

Rainwater can also be used for car washing and other general cleaning tasks around the home.

In commerce and industry
The use of rainwater can really come into its own in business and industry. Not only is water extensively used in a wide range of tasks, but there are often large roof and hard standing areas to catch rainwater. This provides an incentive to invest in rainwater harvesting equipment as business use can offer a relatively short pay-back period.

Rainwater can be used cost-effectively for water-intensive tasks such as dust control, cleaning processes during manufacture, washing vehicles and other specialised cleaning processes such as printed circuit board manufacture, and in agriculture and animal husbandry where farmyards and animal stalls must be regularly hosed down.

In large offices and public buildings, rainwater can be used for flushing toilets and urinals and for cleaning. Facilities managers are increasingly not only insisting these systems are installed on new buildings but looking to retro-fitting the equipment to existing buildings.

Construction Resources can supply individual components or complete systems for collecting, filtering, storing and distributing rainwater. The systems are simple to install in new buildings and need only minimal maintenance by the user.

The filter is available in two models: one replaces a section of the rainwater downpipe; the other is placed underground and integrated into the rainwater drainage system.

Since their invention in Germany in 1989, WISY filters have been successfully installed in hundreds of thousands of buildings. There are areas where including a rainwater harvesting system as standard in new houses has become the rule rather than the exception and indeed it is a legal requirement in The State of Hessen in Germany.

Once collected, filtered rainwater needs to be stored in cool and dark conditions to discourage growth of algae and bacteria. A concrete rainwater tank, buried underground, is ideal. Alternatively, recycled polyethylene rainwater tanks, with capacities from 650 to 12,800 litres can be supplied, to be sited in a cool basement or cellar. Several tanks can be linked together in larger installations, such as hotels, public or industrial buildings. Construction Resources supplies a range of storage tanks to meet most needs.

The rainwater harvesting system includes the Multigo submersible pressure pump which is usually sited inside the tank. It is of exceptionally high quality, is almost noiseless in operation, and only operates when an automatic switch detects a pressure change when a tap is turned on.

Other components include:
. The WISY Floating Suction Filter that ensures that water is not drawn off from the bottom of the tank where very fine sediment may gradually collect.
. Automatic mains backup systems to ensure water is always available even in time of low rainfall.
. Overflows which incorporate anti-rodent and anti- surcharge protection
. Anti-turbulence inflow filter which prevents the stirring up of the settled sediment in the tank
. reinforced rubber suction and ressure hoses

The components are simple but high-precision, reliable, durable, and easy to install and maintain. Visitors to our centre in Southwark can not only see the components needed but will see that we practice what we preach; a rainwater harvesting system supplies our own building’s needs.

Typical rainwater harvesting system

Typical domestic rainwater installation with storage tank in the ground and a pressure pump in the tank

Date published Title File size Document type
Rainwater harvesting
How to save 50% on metered water costs
N/A Product sheet
WISY filter collector
246 KB Product sheet
WISY vortex underground filter
Underground installation for multiple rainwater downpipes
264 KB Product sheet
WISY floating suction filters
254 KB Product sheet
Multigo pressure pump
332 KB Product sheet
Rainwater storage tanks
174 KB Product sheet
Automatic mains back-up
152 KB Product sheet
Rainwater system with small Vortex filter.pdf
CR rainwater harvesting system with small Vortex filter
247 KB Technical data sheet
Rainwater system with standard Vortex filter
CR rainwater harvesting system with standard Vortex filter
270 KB Technical data sheet
Rainwater system to a header cistern
Construction Resources Rainwater Harvesting System to a header cistern with standard Vortex filter
98 KB Technical data sheet
Rainwater Harvesting Control Systems IRM ®-Rainmanager C-Class
248 KB Technical data sheet

To order this product, or to request pricing / quotations, please do one of the following:

- call us at 020-7232-1181
- fax us at 020-7023-3789
- email us at
- use our online quotation request form.

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