Rainwater Harvesting

Rainwater harvesting simply collects the rain which fall onto roofs, then stores it in a tank until required for use. When required, the water is then pumped to the point of use, thus displacing what would otherwise be a demand for mains-water. In the process, a volume of water is kept out of the storm-water management system, thereby helping to reduce flooding risks.

Rainwater harvesting is not a new concept; however, over the last century its use has diminished with the availability of a clean, inexpensive and reliable water source through the mains supply.

More recently, water demand has started to exceed supply, and localised flooding has become an issue. Industry experts are now recognising the important role that rainwater harvesting (also known as rainwater recycling, and greywater recycling) has to play in alleviating both these problems.

Rainwater harvesting systems overview

Rainwater is captured from the roof(s), and brought to a central point, via normal guttering and down-pipes, to enter a storage tank (frequently underground), where it is filtered on entry. A highly efficient and reliable submersible pump delivers the water to a service on demand. Where wished, or a special reason applies, delivery can be to a normal header tank instead.

The size of the storage tank is determined by considering the amount of water available for storage (a function of roof size and local average rainfall), and the amount of water likely to be used (a function of buildings occupancy and function) See services for more information.

Considerations for fitting a rainwater collection system to an existing property

• 1 The external drainage from the roof needs to be modified to bring the water to a central point.
• 2 Access for the tank and excavation is required.
• 3 Internal plumbing is usually required to be seperate out the drinking (incl. bathing) water from the non-drinking water (WC, washing machine & outside tap.

Reasons for rainwater harvesting

• Rainwater harvesting (including rainwater recycling and some versions of grey-water recycling) displaces a large proportion of the water that would otherwise be provided by the mains supply - thus reducing overall water supply costs.
• It can provide an off-mains supply for remote areas.
• It enhance a property and gains Eco-homes rating points.
• It can form part of an attenuation and rainwater management scheme, by reducing storm-water runoff and controlling the flow-rate off site.
• Increasingly planning departments are looking more favourable towards the concept of rainwater harvesting.