Rainwater Harvesting
Rainwater Harvesting is the collection of water that would otherwise have gone down the drain, into the ground or been lost through evaporation. Large surfaces such as roofs or driveways are ideal for rainwater harvesting and can provide up to 100m3 (100,000 litres) of water per year from a medium sized area. This water can be used to flush toilets, water gardens and even feed the washing machine. Rainwater harvesting systems can be installed in both new and existing buildings, and the harvested water used for purposes that do not require drinking water quality. Rainwater harvesting has the potential to save a large volume of mains water and therefore help reduce the pressure on water resources.
Is it for me?
Before deciding whether or not to install a system for home or work, consider the costs of buying, installing and maintaining the system.
- Calculate the volume of rainfall that can be collected from roof areas or driveways to see whether rainwater harvesting can meet your requirements.
- Work out the potential water and cost savings.
For information on how to do this, see our publication, Harvesting rainwater for domestic uses: an information guide (click on link at bottom of the page). While many businesses, housing developments and schools would benefit financially from full scale rainwater harvesting systems, most average households find that the humble water butt is sufficient to meet their needs for garden watering and simple efficiency measures are a much cheaper way to save water in the home.
How does it work?
A typical rainwater harvesting system comprises a collection surface (roof or driveway), some sort of filter and a means of storage (usually a large underground tank). The storage tank for household water use should be sized to hold 5per cent of the rainwater that can be captured in a year or of your annual demand for water, using the smaller of the two figures.
Stored rainwater is not suitable for drinking, but through a separate pipe network it can be used to supply toilets, outside taps and even washing machines. To achieve higher levels of water quality an ultra violet (UV) system can be added. However, these systems use energy and lamps need replacing annually, affecting the cost effectiveness and environmental benefits of the system.
Many systems use a control unit to monitor the water level in the storage tank and display information to the user. If levels drop too low the system switches to the mains water supply and if levels get too high an overflow trap drains off excess water and allows floating material to be skimmed off to a storm drain.
Are there any grants available?
There are currently no grants available for domestic systems, but the Enhanced Capital Allowance (ECA) scheme allows businesses to claim 100 per cent first year capital allowances on investments in technologies and products included in the ECA list of water efficient technologies. Funding for agricultural schemes may be available through your local Regional Develpment Agency (RDA).
Will it save me money?
Rainwater harvesting can potentially give significant financial savings, but these depend heavily on a number of factors:
- The water supply being metered. (Advice on whether metering would be right for you is available from your water provider.)
- The size of the collection area.
- The average annual rainfall (rainfall amounts vary from region to region – the North West can expect double the rainfall of East Anglia in an average year.)
- Whether or not the reduction in metered water consumption translates to a reduction in the wastewater charge – water companies’ policies vary across the country.
How much will it cost?
There is an initial outlay of between £2,000 and £3,000 for a good quality domestic system and plumbing and fitting costs vary. Suppliers of rainwater harvesting systems currently claim savings of up to 50 per cent of water used by the average household. Whilst this is feasible, savings are typically closer to 30 per cent and can be less in some properties.
Due to the relatively low cost of mains’ water in England and Wales and the variability of savings, the payback time for an individual domestic system may be long. Larger projects, such as housing developments, industry and agriculture will have much shorter payback periods and savings could run into many thousands of pounds.
What do I do now?
These questions and answers are designed as a quick guide as to whether a rainwater harvesting system is the right thing for you.
If you want to know more, there is a detailed information guide available by clicking on the Harvesting rainwater link below or for a hard copy e-mail enquiries@environment-agency.gov.uk
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Harvesting rainwater for domestic uses: an information guide (Acrobat, 565KB, 4 minutes)
- 7: Reusing greywater and harvesting rainwater
- Enhanced Capital Allowance Scheme
If rainwater harvesting is not for you or your business at this particular time, there are still many ways that you can cut down your water use with very little outlay. Water butts can be bought for around £20, dripping taps can be fixed for pennies and the amount of water flushed down the toilet can be cut by up to a third. Something as simple as turning off the tap while you clean your teeth can save half a bathful of water per day if done by a family of four.
