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Rainwater harvesting

Filling a watering can with water from a butt

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 areas of most houses are too small to meet all of this demand.

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

If you want to save water and save money there are easier and more economic ways, which with a little thought, will give you good results. Fitting water efficient devices and learning how to save drops is a good way to start.

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 invest in any expensive equipment. The British Standard BS8515:2009 Rainwater Harvesting Systems Code of Practice will tell you that rainwater can be useful for toilet flushing, garden use and washing machines and sets out the standards it should meet. It shouldn’t be used for bathing, dish washing or anything that needs safe and wholesome water quality and you should think carefully before your decide to use rainwater bathing, dishwashing or for use in industrial processes as these may cause greater 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 consider before you install a rainwater harvesting system are:


  • 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 non-potable 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.


  • 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.



  • 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 for businesses

  • If you are a business customer, you can arrange for an on-site assessment to determine whether rainwater harvesting is financially viable for you by contacting Anglian Water Business.


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