On-site wastewater: septic and AWTS systems for unsewered lots

TL;DR

On an unsewered lot the wastewater design is a council approval item that must be resolved before the house position is fixed. The land application area (LAA) is the biggest footprint constraint: setbacks to property boundaries, waterways, and bores can consume 40 to 100 m2 of usable yard, and cut or fill over the LAA after installation is a defect. Conventional septic tanks with absorption trenches are the low-cost option where soil permeability allows; aerated wastewater treatment systems (AWTS) deliver higher-treated effluent and suit tighter sites but carry a mandatory service agreement with quarterly or six-monthly council reporting in most states. The governing design standard is AS/NZS 1547:2012, On-site domestic wastewater management; the approval pathway runs through local council and is administered under state plumbing or local government legislation, which varies by jurisdiction.

When you do this

On-site wastewater planning happens at the pre-design stage, before any site or floor-plan decisions are locked in. The site and soil evaluation must be completed first because the soil category determines the system type and LAA sizing, and the LAA must physically fit on the lot with required setbacks. If the wastewater design can’t be satisfied on the proposed building envelope, the house position changes, not the LAA.

The formal approval sequence follows: site and soil evaluation, system design, council application for a permit to install, installation by a licensed plumber, council inspection (typically pre-backfill), and final approval to operate or use. Post-installation, the owner (or builder on handover) must have a live service agreement in place for any AWTS.

Who’s involved

Wastewater design consultant or engineer (site and soil evaluation report, system design to AS/NZS 1547:2012).
Local council environmental health officer (assesses the application, issues the permit to install, and issues the approval to operate).
Licensed plumber (installs and connects the treatment unit and the LAA; issues a certificate of compliance under the state plumbing framework).
Builder (coordinates siting, protects the LAA during construction, confirms the service agreement is in place at handover).

Steps

Commission a site and soil evaluation. A qualified consultant tests soil permeability (soil category) and records the lot’s slope, site constraints, and proximity to waterways, bores, and boundaries. This report drives system selection and LAA sizing.
Prepare the system design. The designer specifies the treatment unit type and capacity, the LAA layout and area, and the setback compliance check against AS/NZS 1547:2012 Appendix R and any additional council requirements. Design is for domestic flows; AS/NZS 1547:2012 covers systems up to 14,000 litres per week (approximately 10 persons) (verified 2026-06-11, Building Code Hub, AS/NZS 1547:2012 overview).
Lodge the council application. Documents typically required: site and soil evaluation report, system design drawings, manufacturer specifications, land title or survey, and application fee. The council environmental health officer reviews against AS/NZS 1547:2012, any state code of practice, and the council’s own on-site sewage management strategy.
Receive the permit to install. Assessment time varies by council and complexity. Simple septic applications at straightforward rural lots are often faster; complex or constrained sites can take several weeks or longer.
Install the system. A licensed plumber installs the treatment unit, connects the sanitary drainage from the house, and constructs the LAA. Council may require a pre-backfill inspection of the drainage works before the system is covered.
Obtain approval to operate. After installation, the council issues a final approval to operate (terminology varies: certificate of completion, approval to use, approval to operate). This registers the system with the council and triggers ongoing compliance obligations.
Establish the service agreement (AWTS only). Before the approval to operate is issued or shortly after, the owner must have a service agreement in place with an accredited AWTS service provider. Most councils require quarterly or six-monthly servicing with reports submitted as evidence of compliance (verified 2026-06-11, ecoseptic.com.au, Wastewater Regulations QLD and TAS 2026).

System types

Conventional septic tank with absorption trenches. A buried concrete or polyethylene tank for primary settlement; clarified effluent drains to gravel-filled absorption trenches for soil treatment. Lowest capital and running cost. Requires suitable soil permeability and an adequate LAA. Septic tanks need pump-outs typically every 3 to 5 years.

Aerated wastewater treatment system (AWTS). A multi-chambered tank that introduces air and beneficial bacteria to treat effluent to secondary or advanced secondary standard. Higher-treated effluent allows surface or subsurface irrigation of the LAA and suits lots where the soil permeability is too low for absorption trenches, or where a smaller LAA footprint is needed. Requires mains power and a live service agreement.

Sand filters and composting toilets. Sand filter systems add a filtration media layer between the treatment unit and the LAA to further polish effluent. Composting toilets eliminate the toilet waste stream altogether and combine with a greywater treatment system for the kitchen, bathroom, and laundry flows; suitable where water supply is limited and the council and state framework permits them.

Setbacks

AS/NZS 1547:2012 Appendix R provides guidance on horizontal and vertical setback distances for LAAs from property boundaries, buildings, surface water, waterways, and water supply bores (verified 2026-06-11, On-site NewZ, AS/NZS 1547:2012 setbacks and clearances). The appendix is informative, not mandatory: specific setback minima are set by the state regulator or council, and vary. Typical council requirements include setbacks from property boundaries, watercourses, and water supply bores. Confirm the applicable values with council and the designer before finalising the house position.

Builder read

Resolve the wastewater design before fixing the house position. If the LAA can’t fit with required setbacks, the building footprint moves.
Protect the LAA during construction. Cut or fill over a functioning LAA compacts the soil, reduces permeability, and can render the system non-compliant. Mark the LAA on site before earthworks begin and exclude plant and vehicles from it.
Access for pump-outs and servicing. The treatment unit lid and the pump-out point must be accessible by a service tanker. Tanker access clearance (typically 3 m height, firm ground) must be maintained.
Handover package. Pass on: the permit to install, approval to operate, as-installed drawings, manufacturer manuals, and the active service agreement details. The owner inherits the compliance obligations from day one.

Documents needed

Site and soil evaluation report
System design drawings (treatment unit, LAA layout, setback schedule)
Manufacturer product specification
Permit to install (from council)
Approval to operate or certificate of completion (from council)
Plumber’s certificate of compliance
AWTS service agreement (where applicable)

State frameworks

The approval pathway is nationally consistent in structure but administered under different legislation by state:

NSW: Local Government Act 1993; each council develops an on-site sewage management strategy. Section 68 approval required for installation (verified 2026-06-11, ecoseptic.com.au, Section 68 approval NSW).
QLD: Plumbing and Drainage Act 2018; local council issues the permit. AWTS service reports typically lodged quarterly or six-monthly with council (verified 2026-06-11, ecoseptic.com.au).
VIC: EPA Victoria Code of Practice: On-site Wastewater Management guides design; councils assess applications.
TAS: Building Act 2016; Director of Building Control accredits system models; councils issue plumbing permits (verified 2026-06-11, ecoseptic.com.au).

For SA, WA, NT and ACT, confirm the current framework with the relevant state or territory plumbing regulator.

References

AS/NZS 1547:2012, On-site domestic wastewater management (Standards Australia) (verified 2026-06-11, Building Code Hub)
AS/NZS 3500.2:2025, Plumbing and drainage, Part 2: Sanitary plumbing and drainage (Standards Australia)
Wastewater Regulations QLD and TAS: A 2026 Compliance Guide (verified 2026-06-11)
Step-by-step guide to council approval for septic systems and AWTS (verified 2026-06-11)