Greywater reuse

Watering plant with washing up water

If you ever carry a bowl of bathwater outside to water the plants then you are already recycling some of your greywater. Greywater is the used water from baths, showers and hand basins. It can be relatively clean – depending on how much soap, shampoo and shower gel you use – and it can be collected and reused.

At the moment, greywater reuse systems are not common because of:

  • The expense – they can cost a lot to install and maintain and the payback period may be long.
  • The quality of the water – after some basic treatment greywater is usually clean enough for flushing toilets but when left to stand in a greywater storage tank, water quality can to go down as bacteria levels rise.

The British Standard BS8525-1:2010 (Greywater Systems Code of Practice)will tell you that greywater should only be for toilet flushing, garden use and washing machines, as long as it has been treated enough. It shouldn’t be used for bathing, dish washing or anything that needs safe and wholesome water quality, because of potential higher health risks.

Because greywater recycling technology is quite new to the UK, and plumbers are not always familiar with them, we have produced some guidance and advice to help.


Things to think about before you install a greywater reuse system:

Storage tanks and pipework

  • The location of collection, treatment and holding tanks.
  • Greywater system tanks need to be sized to provide a balance between supply and demand whilst maintaining a reasonable throughput.
  • All pipework carrying treated greywater must be clearly marked as a non-potable greywater supply.

Pumps and treatment

Greywater is normally collected at a low level and then pumped to where it can refill toilet cisterns.
Where greywater is used inside the home, biological treatment and disinfection will be required to control bacterial growth and provide 'clear' water. For other uses the degree of treatment will vary depending on the quality of water needed.


  • An alternative non-potable water supply is not a 'fit and forget' technology.
  • Regular cleaning and maintenance and removal of debris from filters and from the biological treatment process is needed.
  • Regular visual inspection of the system components and replacement of filters according to manufacturer's recommendations is required.
  • Ensure mains water top-up is functioning and protected from contamination.
    Regular checks on greywater disinfection in accordance with manufacturer's recommendations.



  • 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.


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