Rainwater Harvesting

The construction of a flood defence depot for the Environment Agency Wales (EAW) at Crosshands provided the opportunity to install a rainwater harvesting system. Constructed in 1999, the building was designed to provide a water resource for use in a number of ways on the site. For the project, a designated team was set up to make the most of an excellent opportunity for the EAW to demonstrate high environmental standards. The project has also provided the EAW with a test bed and demonstration site to gather experience in the application and use of rainwater harvesting systems. The main benefits of the scheme are:

  • Reduced mains water dependence, reducing water bills;
  • Rainwater used where potable water is not required;
  • Test bed and demonstration site for the EAW.

System credentials

The 450 square metre depot roof collects rainfall and feeds an 18 cubic metre underground storage tank. Water entering the system is initially filtered before being passed to the storage tank. Water is then pumped from the storage tank on demand to a variety of uses around the site, including:

  • Toilet flushing via low volume cistern toilets;
  • Vehicle and heavy plant washing;
  • Landscaping requirements including continued pond filling.

All water movement and storage within the system are recorded by data loggers. Electrical consumption is also monitored and recorded, allowing system operational details to be monitored over time. A system schematic can be viewed in .pdf format (right).

Cost savings

The estimated annual savings on mains water and effluent charges have been estimated at approximately £530, providing a 20-year payback on the investment. The tank sizing is an important factor influencing cost and payback. For toilet flushing alone, a 5 cubic metre would have been sufficient, but a larger tank was installed to provide sufficient storage for a variety of rainwater uses. It was estimated that a payback period of ten years could have been achieved with a 5 cubic metre storage tank.

Sustainable construction

Many other features have been integrated into the building to preserve and enhance the environment. All timber used in its construction was sourced from sustainably managed forests in the UK and all internal and external walls have high thermal insulation to reduce the demand for heating. The back-up oil central heating system has fully programmable controls so that it is on only when absolutely necessary