Grey Water Reuse

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What is grey water reuse?

Grey water is the collected wastewater from baths, showers and hand basins. Personal bathing habits will influence the potential quantity available for saving mains water. The most common method of re-using grey water is to carry relatively clean water used for washing or rinsing outside and use on the garden.

At present more sophisticated grey water re-use systems are not common in Dublin for four main reasons:

  • The relatively high cost of the systems especially if retro-fitting.
  • Concerns that the quality of the water may pose a health risk.
  • Requires technical skills to install and provide regular maintenance.


There are many advantages to a Greywater system

  • Reduces the demand on the Dublin Region Water Supply System
  • Reduces demand on the Dublin Region Drainage System
  • If you have a metered account you can significantly reduce your annual water bill
  • Promotes water conservation

It is generally more economic to reduce water use by fitting more water efficient appliances and changing habits and behaviours before considering the use of grey water re-use systems. At present the installation of grey water re-use technology, together with frequent maintenance requirements suggest financial savings will be small, leading to a long pay-back period.

General information

The main factors to be considered before installing a grey water harvesting system are:

  • Storage tanks and pipework
    • The location of collection, treatment and holding tanks.
    • Grey water system tanks need to be sized to provide a balance between supply and demand whilst maintaining a reasonable throughput.
    • All pipework carrying treated grey water must be clearly marked as a non-potable water supply.
  • Pumps and treatment
    • Grey water has to be collected at a low level and then pumped to where it can refill toilet cisterns.
    • Where grey water is used in the home biological treatment and disinfection will be required to control bacterial growth and provide 'clear' water.



Greywater reuse is not a ‘fit and forget’ technology. The following maintenance is required as a minimum:

  • 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 grey water disinfection in accordance with manufacturer's recommendations.


Safety Considerations

Storage tanks should have locking lids and/or bars that keep the children and pets out!

Please make sure that children and pets do not climb on the storage systems and accidentally fall into the storage tank.

It is important to ensure that there is no possibility of contaminating the mains water supply with non-potable water.

For more information

Irish Water Contact Details:

Twitter:  @IrishWater
Telephone: 1850 278 278 (LoCall)
Minicom:  1850 378 378
(For hearing impaired customers with minicom equipment)
Postal Address: Irish Water, PO Box 860, South City Delivery Office, Cork City

Please continue to contact Dublin City Council for information or issues relating to business account queries, surface water drainage and flood management.