The effects of ongoing drought, an increasing population and wasteful over-consumption has put considerable pressure on urban water supplies in most major Australian cities and regional hubs. Ensuring Australia has an adequate and stable supply of drinking water is critical for a healthy population, green neighbourhoods and continued economic growth.

In Australia’s capital cities, domestic water use accounts for more than half of total water consumed. Of this, about 25–50% is still poured onto gardens, so reducing outdoor water use by substituting drinking water with grey water for garden irrigation will substantially reduce domestic water consumption.

Grey water, also sometimes referred to as "graywater" or "greywater", can be defined as domestic wastewater from the bathroom and laundry (water that does not contain human waste). In some Australian states, kitchen wastewater, another name for grey water, however Health Departments do not recommend reusing kitchen grey water without treating it first, as it is generally high in fats, oils and nutrients and can therefore harm plants and soil.

Grey Water Treatment

The best quality grey water for garden irrigation is wastewater from the washing machine, bath and shower. By following some simple precautions, this type of greywater can be safely diverted straight to the garden for the irrigation of plants, lawns and trees.

Regulations for the reuse of grey water vary across states. Please refer to your local council, water authority, state health department or EPA for specific requirements in your area.

Water Recycling Guidelines

In Victoria, generally grey water can be reused for garden irrigation as long as householders adhere to the following EPA Victoria Guidelines:

• Greywater should be reused immediately. Grey water cannot be stored without treatment for more than 24 hours.
• Untreated greywater should be distributed 100mm underground through the garden using sub-surface irrigation only.
• Greywater should be kept within the boundaries of the household generating the water. Do not let greywater run onto neighbouring properties or down stormwater drains.
• Do not reuse greywater if someone is ill in the house or if the grey water contains human waste (such as nappies).
• Do not over-water with greywater or let it pool in the garden. Ensure it is spread evenly throughout the garden and let areas dry out before greywater is re-applied. If rain is falling or expected, do not irrigate with greywater.
• Do not use greywater on vegetables that will be consumed raw if greywater has made contact with the vegetable, particularly avoid root vegetables and leafy greens such as lettuce or herbs.
• Greywater systems must be installed by a licensed plumber.

Grey Water Systems

Greywater diversion systems, such as Waterwise Systems’ Greywater Gardener 230™ , do not require local council approval in Victoria, as long as the system has been installed by a licensed plumber and it has a sub-surface irrigation system. Greywater systems must also meet Australian Standards and have the Watermark Licence. Also look out for the Smart Approved Watermark, which proves that the system will achieve significant outdoor water savings (as accredited products have been analysed by a panel of technical experts).

Grey water treatment systems must be approved by the EPA Victoria as well as by the relevant local council.

When reusing grey water on the garden, householders must be careful to use only garden friendly cleaning products in their washing machine and shower. Products high in sodium and phosphates are harmful to plants and soils. Greywater tends to be more alkaline than drinking water, so it is also a good idea to regularly test the PH in your soil. Bleaches, oils, disinfectants and fats should also be avoided in the garden. Water should not be diverted to the garden if it is more than 40oC in temperature.

To find out more information about grey water, please download one of our factsheets.