Rainwater harvesting: green building features

Water feature

13 March 2015

Rainwater harvesting can work in tandem with other green building features to great effect, says John Griggs

Rainwater has been collected and used in various ways since the beginning of humankind. Primarily, we use rainwater for drinking, by collecting it in reservoirs. In recent times though, when most people rely on water supplies from a tap, there has become a trend for reducing reliance on such municipal services and today 'rainwater harvesting' generally refers to the collection of rainwater for non-drinking water uses in and around a local building or buildings.

Irrespective of the scale of the rainwater harvesting system, the components are generally the same. First, there is some form of collection system, then a filter, a storage vessel, a distribution system, an overflow and possibly a treatment process.

In commercial buildings, rainwater is often used for WC and urinal flushing as well as for garden and lawn   irrigation. Although rainwater can be used for washing clothes and vehicles this is less common. However, one of the main benefits is the reduction of pluvial flood risk by the attenuation of heavy rainfall.

Choosing a system

Rainwater harvesting, greywater reuse or mixed systems should be selected with care to ensure an appropriate choice. One way is to use the new British Standard BS 8595:2013 Code of practice for the selection of water reuse system. Once a system has been selected, reference should be made to the current Code of Practice BS 8515:2013 Rainwater harvesting systems, which covers the design, installation, commissioning, and maintenance of such systems in the UK. Care is particularly needed to identify any non-wholesome supply pipes to ensure health and safety for the occupants and comply with current UK water regulations and bylaws.

Water reuse systems

The range of local planning issues around the UK can lead to opportunities for water reuse systems. For instance, rainwater harvesting systems can often help buildings to comply with planning requirements, for example Marks & Spencer's Cheshire Oaks eco-store development. Water reuse systems can also play a key role in delivering zero-discharge compliance and gaining points on water efficiency compliance regarding BREEAM, LEED and Code for Sustainable Homes Certifications.

When used with green roofs or walls, additional benefits arise. Irrigating green roofs with harvested rainwater provides recreational amenity via terraced or roof gardens, reduces seasonal thermal gain and the urban heat island effect with far lower energy consumption than conventional cooling systems. Irrigated green walls can improve air quality and the visual amenity of a site.

Anthropologie store

Figure 1: Anthropologie, Regent Street

A good example of a zero discharge green roof installation is at Peppa Pig World at Paultons Park in Hampshire. Green walls are usually exterior, as at the Rubens hotel in London’s Victoria, but they can also be internal as in the Anthropologie retail store in Regent Street and the Air France lounge at Heathrow airport.

Expertise for fitting

There is a historical communication disconnect between building designers and M&E contractors, often leaving the installers to sort out the coordination and sequencing on site. This covers both outside groundwork (filter and tank) and distribution system (pumps, controls and secondary pipework). For example, the space to hold the tank is often not provided at the groundwork stage.

The best solution is to involve an expert irrigation installer or specialist rainwater harvesting company at an early stage during the project planning process. This will ensure that the capacity and usage ratios are correct.

Although retrofitting is an option on domestic installations, it is much easier on commercial buildings because most are built with good access to pipework and amendments are therefore not prohibitive. As with any water system, access for maintenance is crucial. Systems are not 'fit and forget'. There are examples of underground tanks access shafts being located in parking areas where cars can hinder access, or even hidden under a road.

Some examples of good design and successful commercial installations include Westfield Shopping Centre, Listerhills Student Village in Bradford and the Everyman Theatre in Liverpool, 2014 winner of the RIBA Stirling Prize.

John Griggs is Director at JPJN Partners and a member of the Sustainable Water Industry Group

This author acknowledges the help of Sustainable Water Industry Group members Zac Ribak, Managing Director at Watermatic and Lutz Johnen, Managing Director of Aquality in the preparation of this article

Further information

  • Related competencies include: Sustainability
  • This article was taken from the RICS Property journal (March/April 2015)