Greywater (also referred to as ‘sullage’) is waste water generated from bathrooms (showers, baths, spas and hand basins), laundries (washing machines), kitchens (sinks and dishwashers) and pools/spas. (Water which has passed through toilets is known as ‘Blackwater’.)
Greywater can be used again, saving you from using new, clean water. However greywater may contain:
- Bacteria, viruses and protoza from nappies and/or soiled clothing, and
- Chemicals from soaps, shampoos, dyes and other cleaning products.
The health risks from these contaminants can easily be prevented by good management practices and by the sensible use of greywater.
And because of the presence of some of these materials in greywater means it can also be a great watering alternative for the garden!
Domestic greywater reuse
Greywater can be diverted to your garden. Greywater diversion devices (GDD) can use gravity or a pump to divert bathroom (not toilet) and laundry water away from your sewerage drain and onto your garden. A GDD must only be used for sub-surface irrigation (no spray irrigation) and an overflow connection to sewer or septic tank must be maintained.
Gravity Diversion Devices
A gravity diversion device has a hand activated valve switch or tap which is fitted to the outlet of the waste pipe. This diverts greywater directly into your garden from areas like your washing machine outlet using gravity. Some gravity diversion systems include a surge tank while others feed straight into the subsurface irrigation system. The flow of greywater is usually activated through a tap or a switch.
Pump diversion devices
This diverts greywater to your garden using a surge tank and pump. Surge tanks capture the water to control the flow of greywater to your garden during sudden surges (but is not used for storage), such as emptying a bathtub. The pump distributes water through the underground irrigation system when gravity is not sufficient. Kitchen greywater is unsuitable for collection in a pump diversion device because it will clog the device causing bad smells and attract vermin.
Chemical composition of greywater
The chemical composition of greywater varies greatly, reflecting the lifestyle of the residents and the choice of household chemicals for laundry, bathing, etc. Greywater typically contains high concentrations of easily degradable organic material, such as fat and oil from cooking, and chemicals from residual cleaning products. The varying chemical composition of greywater means that it needs to be used wisely.
- Greywater tends to be slightly alkaline and this can be harmful to acid loving plants such as azaleas and camellias, but bananas love it.
- Greywater will usually have a low nutrient compared to normal mixed wastewater (sewage). In some cases there can be high con-centrations of phosphorus, but the levels of nitrogen are always low. The amount of phosphorus will depend on the type of products used.
- Environmentally friendly shampoos, detergents and cleaning products should be used to protect soil and plants watered with greywater. Products containing low levels of boron, phosphorus and salt are recommended. Boron can be toxic to plants, some native plants are sensitive to phosphorous while sodium and other salts can damage soil structure.
- Bleaches and disinfectants can kill beneficial soil organisms and damage plants. Avoid using greywater containing harsh chemicals or bleaches, or after washing out hair dye or paint products.
Tips for reusing greywater safely
- Don’t use greywater from washing clothes soiled by faeces or vomit, for example, nappies.
- 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 offensive odours
- Don’t use greywater if other people in the household have diarrhoea or an infectious disease, as this could increase the risk of other people becoming ill
- Keep children away from areas watered with greywater until it has soaked into the ground.