Greywater is used household water sourced from baths, showers, bathroom basins and laundries, but excludes water from the toilet (which is regarded as 'blackwater'). Generally, greywater from the kitchen is not recommended for reuse due to the high levels of organic materials such as oils and fats.
Greywater reuse systems can vary in complexity and can be categorised into two main areas: untreated (bucketing and greywater diversion) and treated (greywater treatment systems). The majority of greywater reuse is at the household level. The following provides some of the considerations for greywater reuse.
- Households may generate significant quantities of greywater but it must be properly managed for reuse in order to protect human health and the environment.
- Untreated greywater (via a simple diversion system) cannot be stored for longer than 24 hours – this may affect irrigation patterns, e.g. overwatering.
- Except for bucketing, untreated greywater may be used only for below ground irrigation (for more information visit the Department of Health's Code of Practice for the Reuse of Greywater in Western Australia).
- The level of greywater reuse in the garden needs to be balanced with the amount of water, solids and nutrients that the plants and soil in the garden can absorb.
- Untreated greywater can contain high levels of sodium, carbonates, boron and phosphates, which may have long-term effects on plants or soils.
- The microbial quality of untreated greywater can be extremely variable and will depend on the volume of faecal material that enters greywater through activities such as washing of nappies or other types of soiled clothing.
- If a house is unoccupied, greywater will not be generated and an alternative means of irrigation will need to be considered.
- Once a domestic greywater system is installed, it becomes the householder's responsibility to ensure it is operated and maintained according to the manufacturer's instructions and Department of Health's guidelines.
- Owners of greywater systems need to be aware of environmental impacts related to system maintenance and household habits, with particular attention to chemicals used in the home (such as cleaning products and laundry detergents).
- Runoff of greywater from the property must be avoided.
Community scale greywater reuse
Where greywater reuse is proposed at community scale in a new development, the following should be considered by the developer:
- Infrastructure requirements for a centralised system. Two additional sets of pipes are needed – one set to collect the greywater from households and keep it separate from blackwater, and another set to pipe the treated greywater back to houses.
- Intended uses and estimated demand (is there sufficient greywater available?).
- Treatment requirements to ensure the water quality is suitable for the intended uses.
- Management of health and environmental risks.
- Estimated cost of implementation.
- Education of and assistance to householders using the greywater scheme.
- Approvals requirements for the intended uses.
- Governance issues surrounding ownership, operation and management of the scheme in the long term.
Greywater can provide a climate-independent resource for reuse, subject to continued occupancy of a house and the number of people in a household.
Greywater generation will vary according to the water usage practices of each individual in the household and the use of water efficiency devices.
The Department of Health Code of Practice for the Reuse of Greywater in Western Australia (2010) provides information on greywater reuse options and volumes.
Bucketing is a simple method to collect greywater directly from the bathroom and laundry with a bucket and apply it evenly on garden or lawn areas.
Greywater diverters are usually gravity diversion devices that coarsely filter greywater. This method only allows greywater to be used for irrigation below ground to reduce the risk of human contact. There are a number of products on the market that range in price depending on their complexity. The filter system generally requires regular maintenance by the homeowner.
Greywater treatment systems collect, store, treat (chemically and/or biologically) and may disinfect greywater to the standards specified by the Department of Health. Depending on the level of treatment, this enables the use of treated greywater for above ground irrigation, toilet flushing and cold water supply to washing machines. Treated greywater can be stored for longer than 24 hours, unlike untreated greywater.
All greywater diversion and greywater treatment systems have to be approved by the Department of Health and must be installed by a licensed plumber.
Community-scale (buildings and new residential developments)
There is growing interest in the collection of greywater from a new office or apartment complex for on-site treatment and reuse in the toilets of that building or watering of small on-site green spaces. The quantities of greywater produced and the intended reuse will depend on the purpose of the building – residential or commercial. A water service provider may be required to provide the service.
New urban developments may include centralised greywater reuse options that collects greywater from individual houses, treats it in a centralised greywater treatment system and distributes it back for irrigation of gardens. A water service provider will be required to manage the system.
The Department of Health's Guidelines for the Non-potable Uses of Recycled Water in Western Australia (August 2011) assist developers with the requirements in getting a non-drinking water scheme (including community scale greywater) approved.
The Department of Health's Code of Practice for the Reuse of Greywater in Western Australia (2010), an application form to construct or install an apparatus for the treatment of sewage, and a list of approved greywater reuse systems are available from the Department of Health website.
Water Corporation: List of waterwise plumbers in the Perth metropolitan area and country areas north and south of Perth.
The Greywater and Wastewater Industry Group, as a collective of water industry professionals, promotes all aspects of water conservation and reuse to the general public, to local and state governments and to the commercial sector. For more information visit their website.