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Grey Water

What is Grey Water?

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Grey water is the collected wastewater from baths, showers, wash hand basins and washing machines (although water from washing machines is increasingly not included in the definition). Personal bathing habits can influence the potential quantity available for saving mains water. The most common means of using grey water is to carry relatively clean water used for washing or rinsing outside and for use in the garden.

Potable (drinking) water is known as white water and and sewage water is known as black water.

At this time sophisticated grey water reuse systems are not widespread in Dublin because:

  • of the high cost of the systems.
  • the high cost of retro-fitting to existing premises.
  • the cost of maintaining the system.
  • until the introduction of domestic water charges there was no payback on the system.
  • of concerns that the quality of the water may be a health risk.

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The of advantages to a Grey water system are:

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  • Reduces the demand on the overall Dublin water supply.
  • Reduces demand on the Dublin drainage system.
  • Non-domestic consumers can substantially reduce annual water bills.

However it is more economical to try reduce the consumption of water by using more water efficient appliances and changing user habits. Currently the installation of grey water reuse technology, together with frequent maintenance requirements means that it not a financially viable option.

If you do decide to install a grey water harvesting system the main items to consider are:

Storage Tanks and Pipework

  • The location of collection, treatment and holding tanks.
  • Grey water system tanks need to be of the appropriate proportions in order to provide a balance between supply and demand while maintaining a reasonable throughput.
  • All pipework carrying treated grey water must be clearly marked not suitable for human use.

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.

The following maintenance is required for grey water systems:

  • 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 for Grey Water Systems

  • Storage tanks must have lockable lids and/or bars to keep the children and pets out.
  • Ensure that there is absolutely no possibility of contaminating the mains water supply with non-potable water.

All rainwater harvesting systems must be approved in advance by the relevant Dublin authority.

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