Eurobodalla Integrated Water Cycle Management Strategy

FACT SHEET 6
Greywater Reuse
Eurobodalla Integrated Water Cycle Management Strategy
What is Greywater Reuse?
Greywater refers to all wastewater from households excluding toilet water (blackwater). It
includes water from the laundry, sinks and dishwashers, and contains less nutrients and
pathogens than blackwater. It can be collected and treated separately using on-site systems.
Greywater is typically reused for irrigation purposes.
The greywater can be treated and disinfected, which can reduce nutrient and bacteria and then
be disposed of through either sub-soil or spray irrigation.
If the greywater is not disinfected, it should be disposed through subsoil irrigation. NSW Health
advises that if the whole greywater stream, (including kitchen wastewater) is being used for
irrigation, it go through a vessel such as a baffled septic tank because it acts as an efficient
grease trap and anaerobic digester before application.
If kitchen waste is excluded, NSW Health advises the greywater stream should go through a
stilling and cooling chamber of about 1 cubic metre before sub-soil disposal.
On-site greywater treatment has the potential to reduce water consumption from other
sources.
A house with greywater treatment needs to be plumbed to separate the greywater from the
blackwater. Treatment is still required for the blackwater, which may range from a composting
toilet to connection to a reticulated sewerage system.
Greywater reuse in sewered areas requires consideration of the NSW Health policy Greywater
Reuse in Sewered Single Domestic Premises (2000).
Examples
Recent UK studies have shown that greywater could be treated to residential reuse grades
using aerated biological filters and membrane bioreactors but the corresponding breakeven
unit water costs were in the order of A$5.00/kL. The development of cost effective residential
greywater reuse technologies is still in the experimental stage.
Benefits
The use of greywater systems on areas connected to the reticulated supply can reduce the
hydraulic loads on the sewerage system and sewage treatment plant.
Water is recycled on-site.
Reduces water bill.
On a small scale (residential) maximises potable water used for potable uses.
Maintains an awareness of water conservation issues through practice.
Potential downstream benefits including reducing or delaying large infrastructure and operating
costs (size of mains and STP augmentations, pump out costs).
Potential Hazards
Household greywater is biologically active and can contain significant levels of bacteria and
other pathogens, which may increase if the greywater is stored for lengthy periods without
treatment. For this reason, health authorities prefer sub-surface irrigation methods.
Another hazard with untreated greywater systems is the potential for clogging of subsurface
systems by the soaps and oils contained in the greywater.
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