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Rainwater Harvesting

Since earliest times, mankind has captured rain in order to provide a simple and accessible supply of fresh water. With the introduction of mains water supply, harvesting methods in the developed world have been largely reduced to the use of garden water butts.

In most buildings, naturally clean rainwater is left to wash away while expensive purified water is used for all applications with only a fraction being used for potable (drinking) use.

In recent years it has become harder to ignore this illogical way of using our natural resources. Water has become a valuable commodity. Increased awareness of the environmental issues surrounding water reserves, drainage and a cultural shift towards sustainability have also meant that rainwater harvesting is more effective and significant than ever before

The Basic Principles

The principles behind rainwater harvesting are simple. Any system has a method of collection (e.g. a roof), a storage vessel (tank) and a delivery facility (be it a simple on/off tap or pipe work system). Integrated rainwater systems still adhere to these elementary steps, but use modern technology to refine the process with automation and filtration.

Integrated Rainwater Harvesting Systems

The rainwater that falls onto a building’s roof is channelled through standard guttering and pipe work. Rather than going into the drain, the water passes through a mesh filter (to remove leaves or debris) before entering a storage tank. When needed, this water is then automatically pumped back into the building and, (after further filtration), is put to use in non-potable applications, such as toilet flushing, laundry or commercial wash down areas. Float level switches within the tank alert an electronic control device to divert to mains supply should the storage tank run empty. The system will always draw on harvested water first. System variations include the use of a header tank and booster sets, but in essence any integrated rainwater harvesting system follows the same process in its operation.

We use water everyday without thinking about it.

On average each person in the UK currently uses about 150 litres of water every day and much of this is wasted. In a domestic situation W.C flushing still accounts for the largest proportion of water use at 33% of average demand. Over 60% of water used in offices is used for W.C and urinal flushing. In both public and private buildings, reducing the amount of water required for flushing W.Cs and urinals result in huge savings. This is especially so when retrofitted into existing buildings where most W.Cs are still flushing with 9 litres of water and many urinals still flush 24 hours a day, 365 days a year.

Did you know that in the UK, rainwater can be used for W.C flushing, washing machine and garden watering, with no further treatment needed?

50% of water in domestic homes and over 60% in offices does not need to be of potable water quality and can be replaced by rainwater.

Not only does rainwater harvesting help with demand on the water supply it also helps with relieving the drains during storms.


The average UK rainfall is 1000mm/per year but most major urban areas receive less than this, with many areas receiving 600mm-800mm/year. The calculation for rainfall is spread across 12 months of the year and it is rare to have no rainfall for longer then 3 weeks (although this does happen sometimes). Regular rainfall is an advantage in that the storage can be smaller then if the rain fell in just one season. As at most properties have a mains water supply rainwater does not need to supply all demand as mains can be used as a back up in times of low rainfall.

If you would like any further information on rainwater harvesting or would like to arrange a survey with a view to installation, please call us on 020 8658 5122 or e-mail on

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