Greywater Retrofit in the Perth Hills in a non-sewered area

This case study describes a greywater reuse system that was retrofitted to an existing 4 bedroom, single story, brick-on-concrete slab house on a 1,000 m² non-sewered block in the Perth hills. Both laundry and bathroom greywater was diverted from the wastewater stream into a greywater diversion system to provide irrigation for lawn and gardens.

The design professional had to ensure pipework was sized correctly to comply with Plumbing Regulations. Appropriately sized Drainage, Waste and Vent (DWV) pipe was used where the greywater diversion device was close to the greywater sources. Greywater collected from the en suite had to travel further and required the use of 100mm DWV pipe.

Greywater System make and model

The GRS-H Filter system from Water Installations, Mundaring is used to filter greywater for whole of house diversion from bathroom/laundry, removing any hair or lint before passing into the infiltration area. Fibre filter bags 500mm long are used and if blocked or too much water enters, a safety overflow device is fitted to direct greywater to the existing sewer or septic tank system as required.


The manifold system used in this greywater case study includes a Biomatt filter and KRain switching device. The Biomatt traps coarse material, such as hair, which may inadvertently pass through the main filter body and be pumped out.

Valve Box & Pump Pit

The filter body is protected by a large valve box (with purple cover) and the lid for the pump pit is foot trafficable.

Cleaning of the filter should occur fortnightly or weekly if excessive laundry and bathroom use has occurred. This device redirects wastewater from the existing system to a disconnector gully return or directly to sewer via a reflux valve.

The previous image demonstrates the filter body before the pump pit and the overflow pipework to the existing septic tank system. Overflow was sent to a Disconnector Gully (DG, or trap) – seen in front of the black pump pit – which was also charged by a single hand basin. A DG is required for at least one fixture so that any backup from the sewer or septic tank system can escape and pass outside of the house.

Greywater Irrigation area

Lawn 70m² and gardens 30m² = total of 100 m². This was laid out as two separate zones as different dripline was used in each area:

  • Tiran dripline was used for the garden areas and trees as it is non pressure- compensating. Each dripper emits 8 L/hr.
  • Netafim XR dripline was used for the lawn irrigation, as it is pressure-compensating. Each dripper emits 2 L/hr and is impregnated with a copper compound to prevent root intrusion,

A K-Rain indexing valve was installed to automatically switch from one zone to another each time the pump was activated.


The manifold system used in this greywater case study includes a Biomatt filter and K-Rain switching device.

Cost of installation of a Greywater System

Approximately $7,000 which included the complete system, all labour, plumber’s charges and power point installation, all irrigation
to lawn and garden beds, Council fees and inspection, testing and commissioning, and handover to client.

Approvals process for Greywater

Approximately three weeks from contract signing to handover. This included a couple 
of weeks for local government “approval to construct”, one day to install the greywater unit with all plumbing and electrics and one day to install the irrigation system, test and commission. Council inspection was arranged for another time and day and handover and training to the clients took place soon after.

Annual water savings

Outcome/Water savings from using a Greywater System

A family of four occupy this house. Based on the Department of Health allowance of 100L/person/ day approximately 400L of greywater could be produced daily, throughout the year on non- rainy days, as system is switched off during rainy periods. Bureau of Meteorology (2019) state Perth receives an average of 80 days of rain, therefore maximum greywater produced (400L x 285 days) is approximately 114,000L (114kL) annually.

I love using Grey water in my garden because it allows me to minimise the use of scheme water in our garden watering regime with only small changes to the type of cleaning products we use in our laundry and bathroom. It also allows me peace of mind every time I take a shower knowing the water isn’t just going down the drain but directly into my beloved garden. 

Andrew Beck
Sustainable Garden Design Perth

Having Greywater go to my garden means my plants get watered every day of the year when I’m home. The water savings in summer are huge. Installing a greywater system at my own new build was a must, along with a Rainwater tank. Putting these systems in during the build process is easy compared to retrofitting, and generally cheaper. ‘Water Capture’ sell, install and service Greywater systems in Perth. 

Mark Harland
Water Capture

WaterCraft service a lot of greywater systems across the metro area and see many gardens thriving on the use of greywater. Frequent watering with traces of soap and nutrients works really well for plants on poor sandy soils. But just as you wouldn’t expect your mains water retic system to run for years without any attention, don’t expect your greywater system to keep running without a service!

Gareth Almond

About The Author

Dr Ross Mars

Dr Ross Mars has had a long involvement with wastewater treatment and reuse, and he has presented papers at a number of national and international conferences, both in Australia and overseas, and has had several papers published in scientific journals. Ross has developed a number of greywater reuse strategies and technologies, and a range of approved products, and has installed these in homes and commercial premises throughout Western Australia. He also manufactures and supplies rainwater tank systems, and installs waterwise gardens, aerobic treatment units for whole-house wastewater recycling and water-sensible irrigation systems. Besides his work in greywater and rainwater tank installations, Ross is one of the most authoritative permaculture teachers, designers and consultants in Australia, and author of four books on the subject and two DVD’s on energy efficient housing design and renewable energy systems for power generation. He has developed accredited permaculture training courses from CI right through to Diploma, and has introduced CI and CII Permaculture as VET programs in high schools.