Rainwater harvesting

Every time we collect rainwater in water butts and containers to reuse in the garden, we’re rainwater harvesting.

If you collect and store it correctly, with minimal treatment rainwater can be used not only for garden watering, but toilet flushing and in washing machines. It could save up to 50% of household water use. But realistically, the roof area of houses are too small to meet this demand.

Industrial premises with larger roof areas offer greater opportunities and can be used for things like vehicle washing.

More sophisticated rainwater systems are available particularly for larger properties but at the moment their use isn’t really that common due to:

• The relatively high cost of the systems.
• Concerns that the quality of the water may pose a health risk.
• The need to have a water meter fitted at your property.
• Uncertainty of the amount of rainwater that can be collected and the size of storage needed to provide a reliable supply during dry weather.

It’s important to work out how much you could save before you investing in any expensive equipment and you should think carefully before your decide to use rainwater bathing, dishwashing or for use in processes as these may cause health issues.

Because rainwater harvesting systems are still quite new to the UK and plumbers are not always familiar with them we have produced some guidance and advice to help.

Things to considered before you instal a rainwater harvesting system are: 

Basics

• What might you use the water for and how much of it you might need.
• The distance between where the water is collected and where you will use it.

Storage tanks and pipework

• The size and location of the storage tank you need.
• The location of a high-level header tank that is usually pump filled from the underground tank.
• All pipework carrying rainwater from the underground tank to the header tank and from the header tank to the end use water fittings must be clearly marked as a rainwater supply.

Pumps and treatment

• An electric submersible pump has to be put in the main storage tank, or a suction pump fitted in a frost-free spot close to it.
• Filters are needed as the first line of treatment for preventing debris entering the holding tank.
• Further treatment may be needed to control potential bacterial growth and ensure 'clear' water if you’re going to be using rainwater for anything other than toilet flushing or vehicle washing.

Maintenance 

• Alternative non-potable water reuse systems are not a 'fit and forget' technology. Regular cleaning and maintenance and removal of debris collected is needed.
• Regular visual inspection of the system components and cleaning and replacement of filters and lamps according to manufacturer's recommendations is required.
• Ensuring mains water top-up is working and protected from contamination.

Regulations

•  All installations need to comply with the Water Supply (Water Fittings) Regulations 1999 in England and Wales.
• The Building Regulations parts G and H apply.
• British Standards BS8515:2009 Rainwater Harvesting Systems Code of Practice which covers the design, installation and maintenance of these systems.

Costs 

• The installation of alternative non-potable water supplies can be expensive, for example domestic systems usually cost more than £2,000.
• The systems have ongoing running, maintenance and replacement costs.
• Payback is likely to be in excess of 10 years.

Carbon footprint

• Due to the energy used for pumping and treatment, greywater reuse may increase your carbon footprint.

On-site assessment

• Business customers can find out more information through our Optimiser technical and efficiency advisory service. To arrange for an on-site assessment to determine whether rainwater harvesting is financially viable for you, please contact the Business Customer Services team.