Greywater systems and technology
There are various methods of greywater reuse; Greywater Diversion Devices and the required system components are the focus of this Guide.
Methods of greywater reuse
The Code approves three different methods of greywater reuse in Western Australia. These include:
A bucket can be used to manually collect shower and laundry water for reuse. There are no restrictions on the amount of water collected in a bucket for irrigation or reuse indoors (e.g. for toilet flushing). This is because volumes are low and, due to the effort involved, application is likely to be restricted to hot weather.
Diversion straight onto the garden
A Greywater Diversion Device (GDD) typically diverts greywater without storage or treatment to the garden via subsurface or substrata (under mulch) drip irrigation, or subsurface trench to minimise potential contact. There are two types of GDD: a Gravity GDD and a Pump GDD, further explained in Section 3.2 of the Greywater Guide Resource Pack. GDD’s must have a WaterMark Licence, which demonstrates compliance with the Australian Technical Specification ATS5200. The emphasis of this Guide is on GDD as they are the most commonly used.
A Greywater Treatment System (GTS) provides a level of treatment so greywater can be used for hand watering, through above-ground sprinklers and for non-potable applications such as toilet flushing and cold water laundry (assuming the required water quality standards are met).
A greywater system is classified as a type of sewage disposal system and therefore must be approved and licensed through the Department of Health (DoH). Once a system has gained DoH approval (as a licenced product), installation at a particular site is administered by local government. Details on DoH approved GDD and GTS can be found via the GWIG website. Conditions of approval may vary depending on the design.
A typical, complete greywater reuse system can consist of three main elements:
1. Greywater drainage collection pipework
2. Greywater unit (Greywater Diversion Devices)
3. Irrigation area
Greywater drainage collection pipework
The greywater drainage collection pipework comprises the network of wastewater pipes, typically PVC, located alongside or under the house. These pipes direct the greywater from the various sources such as shower/s and washing machine to the greywater unit located external to the building and typically below- ground. All work required to connect to the drainage plumbing must be done by a licensed plumber. Refer to the Residential Greywater Ready Plumbing Guidelines (2013), for installing greywater ready drainage plumbing for new buildings. A case study of how to retrofit the drainage plumbing in an existing dwelling is included in this Guide.
There must be an overflow and manual diversion to the main sewerage system (whether utility sewer, septic tank or other form of onsite wastewater system) from any type of greywater unit to allow for diversion of water during periods of winter rain, maintenance; and in the case of overflow or power failure where the flowrate into the system exceeds the capacity of the tank and/or pump.
Greywater unit (GDD)
There are two main types of GDD:
1. Gravity devices
Rather than use a pump, greywater flows from the device into the irrigation field using gravity. These systems are suitable if the property has sufficient slope, bearing in mind that underground systems may still need a pump to raise water from an underground collection point back to ground level for dispersal. The greywater may be dispersed by either dripline or slotted pipe laid in shallow trenches. For dripline irrigation, at least two metres of vertical head pressure is required (refer to Section 4.4 of The Greywater Guide Resource Pack). For piped trench systems a minimal fall of 1:60 is all that is required to disperse greywater into the soil.
2. Pumped devices
Pumped devices often incorporate a surge tank to cope with sudden influxes of greywater, after which it is then pumped to the irrigation field (typically dripline). The surge tank acts as a temporary holding tank and not as a storage tank, as untreated greywater cannot be stored for more than twenty-four hours as prescribed by the Code. Some pump systems are activated by a float switch as soon as greywater enters the tank, while others collect greywater for up to 24 hours and the pump is then activated using an internal timer.
Both gravity-fed and pumped devices should include a filter (or settling tank for gravity systems) at the entry point of the system to remove solids such as hair and lint. This helps to protect the pump and prevent clogging of irrigation drippers or dispersal trenches. Greywater from GDD’s must be discharged subsurface/sub-strata (beneath at least 100mm of soil or mulch) as prescribed by the Code.