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Rain water harvesting

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When water savings are specified, they must justify the system’s environmental costs, says Hattie Hartman

A rain water harvesting system is an easy way to make a project look green, but often money is better spent elsewhere if the aim is to reduce carbon emissions.

It’s a bit like not using a plastic bag. In many projects, the environmental cost of the system outweighs the savings, largely due to the electricity required for pumping the collected water.

These water-saving systems make most sense for sizable projects, such as large retail or commercial projects, schools and for multi-family residential developments, where shared tanks can be used.

A system comprises a tank, filter and control unit, and often a pump. Systems can be gravity fed via a header tank or pumped from the tank to the point of use. A gravity header tank is preferable if the installation permits. Criteria for tank sizing includes roof area and material, building occupancy, water demand and local annual rainfall.

A rain water harvesting system is an easy way to make a project look green, but often money is better spent elsewhere if the aim is to reduce carbon emissions.

Tank sizes range from 3,000 to 6,000l for an individual dwelling, from 30,000 to 50,000l for most schools and frequently up to 300,000l for a commercial installation. Aquality recently installed a 2 million litre tank at Westfield Shopping Centre in West London.

For individual houses, particularly in the drier southeast, Cath Hassell of water consultancy ech2o recommends a 5,000l tank, with external connections to water the garden, rather than more complex internal installations.

The industry has expanded rapidly in the past five years, increasing from a £1.1 million market in 2004 to a forecast £9.2 million in 2009, largely driven by regulatory change such as the upper levels of the Code for Sustainable Homes and the rush to acquire BREEAM credits and LEED points.

Despite this growth, Aquality director Lutz Johnen, who came to the UK from Germany 12 years ago, explains that the market is in its infancy. He frequently conducts CPD, primarily for engineers but also for architects. ‘The UK does not need to reinvent the wheel; this technology is well-established in Germany,’ says Johnen.

Hassell cites the dearth of knowledge among plumbers and explains that further education colleges are just getting to grips with training.


Aquality Trading & Consulting
Aquality offers a hybrid system for medium-sized installations, which uses an underground storage tank inside the building. It has an automatic mains backup in the event of water shortage.

Application Commercial 70 per cent; domestic 30 per cent
Filtration Trident filter using 0.7mm stainless steel grid
Size of tanks From 1,000l
Material Concrete, Polyethylene (PE) or Glasfiber Reinforced Plastic (GRP)
Method of supply Pressurised
Manufacture location Tanks mostly in the UK, controls in Germany
Warranty period Tanks 10+ years; pumps, controls two years
Distributed in the UK from 2004
Extras N/A


Pre-tank and secondary filtration are available from Freerain. They provide assistance with BREEAM and Code for Sustainable Homes calculations. Monitoring systems can display and store consumption data.


Application Commercial 30 per cent; residential 30 per cent; Self-builder and garden systems 40 per cen
Filtration Minimum three stage, down to five microns
Size of tanks 1,000l to 290,000l
Material PE or GRP
Method of supply Gravity and pressurised
Manufacture location UK and Germany
Warranty period PE tanks five years; components two years
Distributed in the UK from 1999
Extras UV sterilisation units


Rainharvesting Systems
Technology first imported from Germany in 1994 for installation at the Green Shop in Stroud, Gloucestershire. Rainharvesting uses special self-cleaning vertical vortex filters – recently installed at St Pancras Station – which oxygenate the water.

Application Commercial 62 per cent; domestic 38 per cent
Filtration Three-stage filtration to 280 microns or UV particulate filter down to 25 or five microns
Size of tanks 1000l to 100,000l
Material PE, GRP and concrete
Method of supply Gravity or pressurised
Manufacture location Germany and UK
Warranty period Components two years; tanks 10 years
Distributed in the UK from 1994
Extras Level gauges; educational monitoring units


Systems include automatic backwashing filtration. The underground tank uses integral vortex filtration with 75mm invert levels across the tank. A domestic system, which uses 50 per cent less energy than a traditional pump, will launch next month.

Application Commercial 55 per cent; educational 35 per cent; residential 10 per cent
Filtration Two or three stage filtration to 50 microns
Size of tanks 1,000l to 300,000l
Material GRP
Method of supply Gravity, direct feed or combination with booster
Manufacture location UK
Warranty period Two years
Distributed in the UK from 2003
Extras Educational monitoring unit and activity pack; visual display units; UV sterilisation units; BMS controls

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