Articles & Case Studies


Posted: Wednesday 17th March 2010

The Queen’s Speech, in November 2009, indicated that water conservation and use is coming on to the political agenda again. By harvesting free rainwater that falls on building roofs, building operators can achieve good pay-back as well as contributing significantly to their corporate environmental responsibilities.

Rainwater harvesting is a well-established, proven technology much more widely used in other European countries than in the UK. In addition, rainwater harvesting is widely recognised as a SUDS solution which can aid the battle against out of control surface water. So how does it work and is it really so high on the sustainability agenda?

Alex Stephenson, Hydro Stormwater Director, says: “A major use of treated mains drinking water for most businesses is flushing toilets; even a regulated flush averages five litres a time. This makes it easy to calculate the waste of expensive drinking water that is thrown away by an office full of people during working hours. These days, sustainability is very much a public issue, and introducing environment saving measures wherever we can is important.

“Rainwater Harvesting systems are easy and cost-effective to install, especially in a new or refurbished building or extension. Free rainwater can be used for a variety of tasks such as vehicle washing, yard washing and even for non-hygienic manufacturing. Systems can be scaled to the building size, and can provide a payback on capital purchase within a few years, as well as your metered mains water bill being substantially reduced.”

Rainwater harvesting collects rainwater from the building roof and stores it in an underground tank, usually sited under a car park or yard, and pumps it on demand to toilets, taps, hoses and other points of use. The investment can be at least as favourable as advanced energy management measures, because the payback is often better than the five to fifteen year ROI frequently quoted for increased insulation, new boilers and airhandling systems.

Holding back the floods

Rainwater Harvesting can also play a vital role as part of flood risk management by holding back stormwater runoff at the point of falling during periods of heavy rain. As an integral part of Sustainable Drainage Systems (SUDS), rainwater harvesting can help reduce peak flows and associated stormwater runoff volumes.

SUDS systems aim to mimic the storage and controlled release of rainwater that trees and soil achieve in the natural landscape. Where the natural landscape has been developed, for instance through building development, with roofs, roads and car parks, impervious, hard surfaces are substituted for vegetation. Rainwater can run straight off these surfaces, channelled via storm drains to the watercourses. Uncontrolled rain, as in a storm, will lead to high peak volumes which may overtop river banks, causing flooding.

The philosophy of SUDS is that by holding back rain where it falls, through storage and controlled release or infiltration, it is stopped from reaching the rivers and lakes in volumes which overtop existing flood defences. It is this control of stormwater volume, through techniques which require minimal maintenance and low lifetime costs, that form the basis of sustainable drainage systems, widely known as SUDS.

By using stormwater management techniques, a drainage system can mimic the action of a natural landscape. There are many SUDS relevant techniques which can be used separately or in harness depending on the location and requirement.

Rainwater harvesting can make an important contribution to retaining rainwater that falls on roofs and, through recycling it through a building, can delay or prevent its release into watercourses and the environment.

Conserving and controlling

Alex Stephenson continues: “Rainwater Harvesting is rapidly becoming accepted as a desirable feature of sustainable buildings. Commercial rainwater harvesting systems need to be designed to meet the individual needs of the user, and it’s important to consider design issues at an early stage. It’s important to consult a supplier with a comprehensive design and advisory service to ensure water saving opportunities are maximised for each building.

“Rainwater harvesting has a demonstrable payback and many installations will pay for themselves in just a few years. On larger commercial applications it can be possible to achieve quantity savings on mains water in the order of 35-40% with commensurate savings on commercial water rates.

“Rainwater harvesting also helps meet planning consent for developments by controlling stormwater discharge from roofs to the mains, and thus helps reduce the flood risk of storm water runoff from hard surface developments.

“The increasing awareness by Government and planning officials of the major role surface runoff plays in flash flooding, like in 2009, means that there will be increased pressure to control all sources of stormwater.”

Cumbrian school

Engineering and environmental consultant, Waterman Group, recommended rainwater recycling for the new classroom block at Trinity School, Carlisle, to enhance sustainability and meet environmental targets from Cumbria County Council. As a result, Hydro International’s StormBank® Pro rainwater harvesting system was installed, enabling rain collected from the school roof to be used to flush toilets.

The StormBank® Pro brings water savings and sustainability within the reach of every building from small offices through to schools, hospitals and care homes. By using collected rainwater, instead of expensive treated drinking water, StormBank® Pro provides building users with a sustainable water supply which can be used in a range of applications from toilet flushing and garden watering, through to vehicle and yard washdown.

“Rainwater recycling is an important contributor to a high sustainability design strategy, so we recommended its incorporation”, commented John Pickering, associate director of building services, Waterman Group. “The StormBank® Pro system also helped us to aim for a very high Building Research Establishment Environmental Assessment Method (BREEAM) rating.”

Located in a high rainfall area in the North West, a 25,000 litre main tank was recommended by Hydro to accommodate the volume of water from the new 95 metres by 25 metres classroom block. The storage was teamed with a StormBank® Pro 3-B 40-80 pump, connection set and ancillaries.

Matching size to requirement

Commercial harvesting systems are not an off-the-shelf solution, and many design issues need to be identified and quantified in order to provide the most efficient and effective design. It therefore becomes important to consider these issues at the earliest design stage so that key deliverables can be achieved. Hydro International offer a comprehensive, client-sensitive design and advisory service on all commercial rainwater harvesting issues.

Hydro’s expertise in configuring a StormBank® Pro system to meet the specific needs of building users is based on extensive experience of the requirements of different types and sizes of application. Each system comprises a storage tank, water filter and control panel offering easy installation and minimal maintenance at competitive prices.

The largest commercial StormBank® Pro system can be computer connected to the building’s management system. All StormBank® systems have mains water back-up for occasions when rainwater runs low.

Tel: 01275 878371,
Fax: 01275 874979,

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