Greywater design and technical application

A correctly designed, installed and maintained greywater system can provide numerous benefits to both the homeowner and environment. Engaging the services of a greywater professional can ensure that the installed system performs efficiently, provides an adequate amount of water to the garden, and satisfies the requirements within the Code.

In this section examples and case studies are provided on the design and technical considerations for an existing home and a new home, taking into consideration the information provided in the previous sections. Most of the examples of system design included here assume that all available greywater is connected. It is possible to have shower only or laundry only greywater systems where the total volume of water would be proportionally reduced.

Feasibility of a greywater system

Key feasibility considerations include:

Available garden area and number of household occupants.

Available budget. A typical whole-of-house system witth irrigation can cost around $5000 excluding dual plumbing.

Time to plan and implement a system. Pipework for a new house will need to be laid before the concrete slab.

Expert advice. An experienced greywater professional can advise on an appropriate system layout and ensure the whole design (including areas to be irrigated, dimensions of garden beds, proximity to garden beds/pools/property boundaries) complies with the Code.

Existing home

Retrofitting an existing home requires professional advice on design to work with the existing plumbing and existing garden layout.

Use in older homes with through-wall waste pipes

The the G-flow unit is also suitable where the waste pipe comes out of the wall rather than under the slab – for example behind the laundry trough in an older home. In this case, wastewater can simply gravity feed into the unit.Use in older homes with through-wall waste pipes

A summary of greywater system design criteria set by the Code

Untreated greywater must not be stored for more than 24 hours, as it may start to smell.

Appropriate setbacks from buildings, property boundaries, paths etc. must be used to apply the water in the required areas.

Untreated greywater must be applied to the garden by subsurface/substrata irrigation (i.e. no sprayers can be used).

Avoid ponding of greywater, so it is quickly absorbed by the soil.

An overflow and diversion point into the primary sewerage system is required (in case of malfunction, or when the systems is not in use).

Greywater is to be confined within the property boundary and is not permitted for use on verges.

About The Author


Greywater & Wastewater Industry Group. We are a group of water industry professionals who are active in the design, research, manufacture, installation and servicing of greywater and wastewater treatment systems. GWIG is a non-profit organisation which was formed in late 2010 in order to provide a united voice for a WA industry that is largely unsupported and under-acknowledged for the important work that it does.