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Using greywater on the garden

GreySmart: Australia's complete greywater resource
ATA Smart Water Fund Study: comparing greywater systems
Greywater gardening advice from Sustainable Gardening Australia
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This is a great option for supplementing garden watering because it doesn’t rely on drinking water and isn’t affected by water restrictions. However, it does need to be managed carefully. Water can be recycled from your shower and washing machine but because it contains some bacteria, detergents, cleaning agents and waste material, it isn’t suitable for all garden uses.

The preference for greywater sources to use in the garden is based on the quality of the water and possible chemicals in it. Use the vegetable rinse water first, then bath and shower water, then laundry rinse water and laundry wash water last.

Here is a general list of garden greywater use "dos and don'ts" which apply to all residents. Print it and keep in a safe place as a handy reference source.

Do
  • Use low phosphorus detergents.
  • Only use untreated greywater in appropriate areas of the garden.
  • Apply diverted greywater to the garden by a below ground seepage pipe. This will reduce human exposure to the water.
  • Use greywater only during prolonged warm, dry periods and use only what you need to meet your plants' water requirements.
  • Ensure greywater is diverted to the sewer during wet periods.
  • Install a diversion system that is 'fail-safe', where the greywater will automatically be diverted to the sewer if the greywater system blocks or malfunctions.
  • Stop using greywater if you smell odours and your plants do not appear to be healthy.
  • Wash your hands after watering with greywater and after gardening in greywater irrigated areas.
  • Use less fertiliser when irrigating with greywater.
  • Ensure greywater does not contaminate any source of drinking water. Extreme care must be taken to ensure there is no cross-connection between the greywater re-use system and the drinking water supply.
Don't
  • Never water vegetable gardens with greywater if the crop is to be eaten raw.
  • Never use greywater that has faecal contamination, for example, wastewater used to wash nappies.
  • Never store untreated greywater for more than 24 hours.
  • Never drink greywater or allow children or pets to drink or play with greywater.
  • Never allow greywater to flow beyond your property boundary or enter stormwater systems.
  • Do not use kitchen wastewater (including dishwashers) - it contains highly concentrated food wastes and chemicals that are not readily broken down by soil organisms.
  • Do not allow greywater to pool or stagnate as this will attract insects and rodents, which may transmit disease.

Greywater Diversion Systems

You generally do not need permission to bucket water from the shower or laundry onto your garden. However any plumbing system that diverts greywater from the shower and washing machine should always be checked with your local Council. You also need to have a licensed plumber conduct any alterations to your plumbing.

There are a number of products to divert greywater to your garden available from your local garden centre, hardware or plumbing shop. Usually people divert washing machine (final rinse) water and shower water onto garden beds through existing plumbing inspection hatches or open doors or windows. Greywater must not be stored for longer than 24 hours. If you do any plumbing you should use a licensed plumber.

If you divert from the washing machine make sure:

  • The diameter of the diversion hose is not smaller than the washing machine hose.
  • The hose does not kink.
  • The water does not have to travel uphill and is not significantly slowed by travelling through the pipe (e.g. a very long connection) or it may permanently damage the washing machine pump or burst the hose connection and flood the laundry.

Some systems are now available that do not treat greywater, but store it for less than 24 hours for irrigation on your garden. Generally if you are going to use greywater on the garden it's best to distribute it via sub-surface irrigation systems (drip tubes under mulch, drip spikes, etc).These systems generally need government approval and may require a permit from your Council.

Greywater Treatment Systems

There are many systems available for treating and storing greywater. These systems treat greywater to a standard so it can be stored indefinitely and used inside the house, but not for human consumption. These systems are usually priced at more than $5,000 and need to be installed by a plumber with prior approval from the EPA. A septic tank permit from your local Council is also required. 

Although this may seem like an expensive alternative, a permanent greywater diversion system provides your home sewerage main overflow greywater system with a constant supply of usable water, unlike rainwater, which is seasonal. You can use this treated water to refill your toilet (14 per cent of normal household use) all year round or supply your washing machine (16 per cent of normal household use). Generally if you plan to use this water on the garden, the treated water needs to be connected to sub-surface irrigation systems. 

If you are designing a renovation or a new house call a Green Plumber and discuss plumbing options to make sure you can access greywater re-use opportunities as part of the design.