Wastewater is the used water from households and business that is disposed of through the sewerage network (or into septic tanks in some areas). Wastewater is 99.97 per cent water as the majority is sourced from showers, baths and washing machines. The remainder is dissolved and suspended matter.
Treated wastewater is discharged from a wastewater treatment facility after it has passed through treatment processes to reduce its nutrient and bio-chemical load.
This can provide a secure and sustainable source of water that is climate-resilient unlike 'traditional' water supply options. Further treatment may be required, depending on the intended use, if treated wastewater is considered as a non-drinking water source option.
The viability of a wastewater reuse system will depend on factors including:
- availability and intended uses, estimated demand and back-up (contingency) water source
- required level of treatment for intended uses
- management of health and environmental risks
- site limitations, including proximity to public drinking water source areas or to conservation category wetlands
- land requirements for infrastructure and storage (below or above ground)
- cost of implementation and ongoing management of the scheme
- governance issues surrounding long-term ownership, operation and management
- community awareness and acceptance
- required approvals.
In some proclaimed public drinking water source areas irrigation with treated wastewater is considered an incompatible land use. The Department of Water's regional offices can provide further information on the location of public drinking water source areas and on the land-use compatibility within these areas.
The volume of wastewater available for recycling will increase with population growth. Consequently, wastewater recycling is an important and significant fit-for-purpose water supply option.
Treated wastewater from wastewater treatment plants
Wastewater reuse is likely to be most economical in the vicinity of an existing wastewater treatment facility, after it has had its nutrient, biochemical and pathogen loads reduced. Further treatment may be required depending on the intended end use.
Sewer mining involves extracting and treating wastewater for use, before it reaches the wastewater treatment plant. Sewer mining is a complex option requiring the construction of a local wastewater treatment facility, such as a membrane bio-reactor, to treat the raw wastewater to fit-for-purpose quality, storing and delivering the recycled water to the end-user and managing residuals.
For more information, availability and conditions of using wastewater from existing treatment plants or via sewer mining visit the Water Corporation's H2Options website which includes a water balance calculation tool and useful factsheets.
Supply and storage options
Irrigating public open space
Treated wastewater can provide a climate-resilient water source for the irrigation of parks, public gardens and golf courses, especially where the potential reuse site is in the vicinity of an existing wastewater treatment plant. Alternatively, access to untreated wastewater from a sewer mains could be considered, which will require on-site treatment by the proponent. Both options require adequate storage, and distribution and irrigation infrastructure.
Subject to availability, the Water Corporation will provide treated wastewater for community benefit free-of-charge at the wastewater treatment plant boundary. With relevant environmental and health approvals, this water could be used to irrigate public open spaces, parks, ovals and recreation areas. The proponent –a developer or local government – will need to pay for any additional treatment, piping and transport costs.
In regional Western Australia, irrigating public open space with treated wastewater is common practice and has provided a cost-effective irrigation and wastewater disposal option for many years, while maintaining outdoor lifestyle and amenity.
Community-scale (third pipe) recycled water systems
Treated wastewater from a water recycling plant is transported via a third pipe (purple) scheme to multiple users for watering lawns and gardens and for in-house non-drinking uses, such as toilet flushing and the cold water tap in laundries. The scheme can include irrigation of public open space within the community. This is most viable in new urban developments where the required pipelines can be installed together with other below-ground infrastructure.
Service provider requirements
Third pipe schemes require a water service provider and, depending on the scale of the operation, the provider will require either a licence to operate the scheme under the Water Services Act 2012 or need to apply for an exemption from licensing. Contact the department's Water Industry Policy for initial advice whether the proposed service would qualify for a water services licensing exemption and on the process for obtaining an exemption.
A developer needs to consider who will own, operate and maintain the non-drinking water scheme now and in the future to ensure that it is sustainable. It is recommended that a developer identifies and consults with the preferred water service provider early in the planning process. All personnel involved in the operation of a non-drinking water system need to have the appropriate skills and training to undertake their responsibilities to ensure a long-term safe and reliable management of the system.
In accordance with the Water Services Act 2012, all persons providing water, sewerage, drainage or irrigation services in Western Australia must either obtain a water services operating licence from the Economic Regulation Authority (ERA) or an exemption from the licensing requirement from the Governor, provided it is not contrary to the public interest.
Aerobic Treatment Units for single households in unsewered areas
Aerobic Treatment Units (ATUs) are a more advanced alternative to conventional septic tanks and provide an improved quality of wastewater treatment for single dwellings in unsewered areas. ATUs must be approved by the Department of Health and inspected by the local government. A permit to use the apparatus is issued by the local government prior to its use. The chlorinated effluent from ATUs may be used to surface irrigate garden areas but can only be used below grassed areas. It is not approved for any use in vegetable gardens.
A Code of Practice, a list of approved ATUs and required application forms and guidelines are available from the Department of Health website.
Managed aquifer recharge
There is growing interest in opportunities to inject or infiltrate treated wastewater, sourced either from wastewater treatment plants or sewer mining, into an aquifer for later abstraction to irrigate public open space, horticulture or for other reuse. However, managed aquifer recharge may not be feasible on all sites, due to hydrogeological, environmental or cost limitations.
For more information see the department's managed aquifer recharge information.
Department of Health: Guidelines for the Non-potable Uses of Recycled Water in Western Australia (2011) are based on the Australian Guidelines and assist proponents with the requirements in getting a recycled water system approved.
Department of Health: Code of Practice for the Design, Manufacture, Installation and Operation of AerobicTreatment Units (ATUs) (2001) and additional guidelines for water recycling in unsewered areas.