Greywater is wastewater generated from:
- bathrooms, including showers, baths and hand basins
- laundries, including washing machines and troughs
- kitchens, including sinks and dishwashers.
Kitchen wastewater can contain food particles, grease, oils and fats and its use is not recommended, particularly without treatment.
Installation of permanent greywater systems requires an approval from the local council and the Office of the Technical Regulator.
Potential risks when using grey water
Owners and users should clearly understand the potential risks to public health and the environmental impact of greywater that can be caused through improperly designed, installed, and maintained systems.
Use of greywater over a long period of time without proper management of the sources of contamination or the irrigation system may lead to further negative impacts, which may result in pooling and runoff.
Public health risks
Greywater may contain significant levels of disease causing organisms particularly where household members are suffering from a gastrointestinal illness.
The disease causing organisms in greywater are mainly transferred through:
- contaminated hands
- inhalation of irrigation spray
- contact with broken skin.
Other ways include indirect methods which include:
- contact with contaminated items such as toys, garden implements, grass or soil
- transmission by pest vectors such as rats, mice, flies and cockroaches
- transmission by family pets.
Reducing the risks
There are a number of requirements which must be followed in order to reduce the risk to public health, including:
- Untreated greywater must only be used via subsurface irrigation. Subsurface irrigation systems reduce exposure to humans, pets and other animals which may otherwise come into contact with the untreated greywater and potentially transfer disease causing organisms.
- Specific setback distances from buildings, boundaries, wells, bores, watercourses, swimming pools and rainwater tanks are required to be met for all irrigation systems. This is to prevent contamination and transmission of disease. See the SA Health On-site Wastewater Systems Code April 2013 (PDF 2901KB) for more information.
- Greywater must not be used to irrigate fruit, vegetables, or areas where fruit can fall to the ground and be eaten.
The following points may help to minimise environmental impacts from greywater use:
- Environmentally friendly shampoos, detergents and cleaning products should be used to protect soil and plants watered with grey water. For useful information on laundry products, see the Lanfax Laboratories website.
- Products containing low levels of boron, phosphorus and salt should be used. Boron can be toxic to plants, some native plants are sensitive to phosphorous while sodium and other salts can damage soil structure
- Washing machine rinse water has lower concentrations of detergents compared to wash water. If wash water is used it should be diluted with rinse water
- Bleaches and disinfectants can kill beneficial soil organisms and damage plants. Avoid using greywater containing harsh chemicals or bleaches, hair dye or paint products
- Prevent pooling and runoff of greywater onto other properties, into watercourses and the stormwater system. Pooled greywater can turn septic and produce offensive odours.
- Greywater tends to be slightly alkaline and this can be harmful to acid loving plants such as azaleas and camellias.
- Monitor areas and plants irrigated with greywater. If there is visual evidence of damage you may need to modify watering practices, try a different or bigger irrigation area, or reduce the amount of water used.
- Soils in many parts of Adelaide have a high clay content. Clay soils tend to be more susceptible to build up of salts and have low permeability. Extra care should be taken when using greywater in areas of clay soils to avoid long term damage
- Don’t over-water your plants - greywater shouldn’t be used to irrigate more than you would with other sources of water. Plants are susceptible to waterlogged soil.
Temporarily diverting greywater
Manual bucketing onto lawn and garden areas using water from the bathroom or laundry, or temporary use of a hose manually fitted to the washing machine outlet hose, is permitted subject to the following advice:
- don’t use greywater from washing clothes soiled by faeces or vomit, for example nappies
- don’t use greywater if others in the household have diarrhoea or an infectious disease, as this could increase the risk of other people becoming ill
- don’t store untreated greywater for more than 24 hours, as bacteria and organic contaminants in greywater will cause it to turn septic and produce strong and offensive odours
- don’t use greywater to irrigate fruit, vegetables or areas where fruit can fall to the ground and be eaten
- avoid splashing of greywater and wash your hands before eating, drinking or smoking
- keep children away from areas watered with greywater until it has soaked into the ground.