Grey Water

What is Grey water

Wall mounted Grey water unit

Grey water is the water from your bathroom sinks, bath, shower and laundry. It is distinct from the water from your toilet and kitchen sink which is known as black water. Both types of water fall under the Health Authority’s jurisdiction and there are a number of requirements that must be met when installing a system.


Most popular with retrofits; a wall mounted grey water unit takes the water from the washing machine, filters it and gravity feeds it through lilac drip line to a garden bed.  Provided your washing machine is on an external wall installation is straightforward.

New houses

If you are building you can dual plumb your home and use all of the grey water on your garden.  If you provide us with your house plan we can provide the builder with a plumbing diagram with his and our responsibilities, it is important to do this early on in the building process. Even if you don’t connect the grey water system straight away it is an idea to dual plumb ( grey water ready ) as it is an expensive process, if not impossible, after the house is finished.

How much garden can I Irrigate

The area of garden irrigated is constrained by the Health Authority and an average 4 bedroom house will need about 100m2 of grey water garden regardless of the number of occupants, refer to examples.  Garden beds need to be wide enough to allow clearances from the drip line to the fence and house. You need to have an idea of your garden layout before we can design the irrigation; we can provide a landscape design if you need one. Refer to our Landscaping page.


Grevilleas with grey water irrigation

The plans need to be submitted to the council and the health department with information about the system used. We ensure all the requirements are met and apply for the appropriate permits for you.  Most Councils have a $220 fee payable with lodgement of the application, we add $75 to this for our administration costs.

Will my plants be affected?

Most plants will thrive in grey water provided you are careful what you put down the sink. No bleach or turps. There is a large range of no phosphorous low salt environmentally friendly detergents on the market.

What happens when I go on holiday

We install a top up on all of our systems which will allow you to use scheme or bore water to irrigate when you are on holidays or if your water use is not sufficient to provide enough water in summer.

Can I water turf

 You can water turf with grey water but we do not recommend it if you have sufficient garden beds.

Cleaning and Maintenance

All grey water systems need the filters cleaned regularly, simply hose them out on to your garden. The system will need flushing once a year which we can do for you in our winter service plan.

Dual Plumbing- Grey water ready

Dual plumbing means to plumb the black water (toilet and kitchen sink) and grey water (everything else) separately.  Traditionally when a house is built all the waste water flows in to a single pipe that runs down the side of the house, trying to separate the water pipes after the house is complete can be very expensive if not impossible.  Dual plumbing while building is relatively inexpensive as they can easily put 2 pipes in the same trench, it is a good idea to do this even if you don’t plan to get grey water straight way. The additional “builders “ cost at the build stage to make the house grey water ready is about $ 2,000 extra for the electrical GPO, grey water drains and reflux valve installed by the builder. Then add the cost of the grey water system and grey water irrigation

Grey water system

Grey water pit

The grey water system (surge tank) sits near the sewer inlet; it receives the grey water and directs it into the irrigation system.  Just before the grey water tank is a ‘Jump Up’ bypass and a reflux valve which diverts the grey water into the sewer if the tank is full or the pump stops working. Water is not held in the surge tank; it is pumped into the irrigation system as it enters the tank. Grey water should not be stored as it has a high level of contamination; if it is used straight away (less then 24hrs) it reduces the risk of pathogens growing in the water. The water is filtered inside the tank to remove large particles, it is important to clean the filters as recommended by the manufacture.   Download our PDF for more information and a diagram. All the systems we use are approved for use in WA.

An electrical GPO must be located near the unit for the Pump, preferably on a separate circuit.

All our grey water irrigation systems have a top up from your bore or mains water. This means when you go away or there is insufficient water use within the house to water the garden your plants will not die. It also helps flush the tank and keep it clean. The top up must have an air gap between the water outlet and the grey water tank inlet, this type of connection is known as a tundish.


When the water leaves the tank it goes though an index valve, these ingenious mechanisms slowly rotate as the water passes through them giving even watering to several different areas.  For a 4 bedroom house a 100m2  irrigation area is required, we would usually break that area into 3 equal parts, depending on other factors like sizes of garden beds. The irrigation must be sub surface and covered in 100mm of mulch, lilac pipe is used so it can be easily identified. Flush values are placed at the end of runs so the irrigation pipe can be flushed annually to prevent clogging.


A summary of the relevant Health department regulations for grey water irrigation.
Download this PDF for full details.

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