Buying a house with a septic system: what to check before you sign
Written by Septic Help editors Last reviewed
A septic system is the one part of a rural or acreage property that a standard building-and-pest inspection barely touches — and it's a five-figure item if it's failing. Before you sign, you want answers to four questions: is the system approved, has it been looked after, how old is it, and is the ground it drains into still working? Here's how to get each answer, and what to ask the vendor along the way.
1. Check the approval and registration with council
Every on-site wastewater system should exist in a council file: an approval to install, an inspection record from when it went in, and — in some states — a current operating approval. In NSW, councils approve the installation, alteration and operation of on-site sewage management systems under section 68 of the Local Government Act 1993, and many require the new owner to apply for an approval to operate within about three months of settlement (Byron Shire Council, for example, spells this out on its on-site sewage management page). In Victoria, councils issue a permit to construct or install and an approval/certificate to use under the Environment Protection Act 2017. In Queensland, on-site sewerage work is approved under the Plumbing and Drainage Act 2018.
Ask your conveyancer to request the council's file on the system, or ring the council's environmental health team yourself. You're looking for: an approval matching the system actually in the ground, no outstanding rectification notices, and no record of failed inspections. A system with no council record at all is a red flag — councils can require unapproved systems to be brought up to standard at the owner's cost, and after settlement that owner is you. Our state approvals guides explain who to call in each state.
Some councils will inspect for you
A number of NSW councils offer a formal pre-purchase inspection of the on-site system by an environmental health officer, typically reported within 7–10 working days. Byron Shire lists the service at $761. If the vendor won't agree to access, that tells you something too.
2. Service records and pump-out history
A conventional septic tank should have been pumped out roughly every 3–5 years; ask for receipts or the contractor's name. An aerated wastewater treatment system (AWTS) is a bigger ask: it has pumps, blowers and a mandatory quarterly service contract in most states, so there should be a stack of service reports — many councils receive copies directly. No records usually means no servicing, and an unserviced AWTS is a system living on borrowed time. See our guides to pump-out frequency and AWTS servicing requirements for what "looked after" should look like on paper.
3. Tank age and system type
Find out what you're actually buying: a conventional tank with absorption trenches, an AWTS irrigating treated water, a sand filter, or something older and stranger. The type sets your running costs — a conventional system costs a few hundred dollars every few years, while an AWTS runs to several hundred dollars a year in servicing plus power. Age matters most for the concrete: tanks commonly last 30–50 years, but baffles corrode and lids crack well before that, and absorption trenches typically last 15–25 years. A 30-year-old system that's never had trench work is due, whatever the vendor says.
4. Walk the land application area
The trenches or irrigation area are the most expensive part of the system to replace, and the easiest to check for free. Walk the area (ask where it is — the council plan will show it) and look for the classic signs of failure: boggy or spongy ground in dry weather, effluent surfacing, sewage smells, and a stripe of suspiciously lush green grass. Also note what's sitting on top of it — sheds, driveways or a pool over the land application area are a problem, and the area can't later be built over without redesigning the system. If you're planning to extend the house, remember the reserve area: many approvals set aside land for future replacement trenches.
5. Questions to put to the vendor
- When was the tank last pumped out, and by whom?
- Is there a current service contract (for an AWTS), and can it be transferred?
- Has the system ever overflowed, backed up or been repaired? What was done?
- Where exactly are the tank, trenches and any reserve area?
- What does the system cost to run in a typical year?
- Has council ever issued a notice, or failed the system at inspection?
- Was any alteration — extra bedroom, second bathroom, granny flat — done with council approval of the wastewater side?
Vague answers to the last two are your cue to order a proper pre-purchase septic inspection and make the contract subject to it.
State differences in disclosure
Don't assume the contract will tell you. In Victoria, the vendor's section 32 statement under the Sale of Land Act 1962 must disclose that the property is not connected to mains sewerage — courts have allowed purchasers to walk away where this was missed — but it doesn't have to volunteer the system's condition. Queensland's seller disclosure statement (Form 2, mandatory since 1 August 2025) covers title, zoning and notices, yet expressly does not require disclosure of structural soundness — the state's seller disclosure scheme guidance is clear that condition is the buyer's problem. In NSW there's no general obligation to disclose the system's health either; the buyer's protection is the council file and their own inspection. Everywhere in Australia, the working rule is the same: disclosure tells you the system exists, not that it works.
Common questions
Can I make an offer subject to a septic inspection?
Yes, and on an unsewered property you should. Ask your conveyancer to add a condition making the contract subject to a satisfactory on-site wastewater inspection, the same way you would for building and pest. In auction states you'll need the inspection done before auction day instead.
What if the system was never approved by council?
Price it as if you're replacing it. Councils can require unapproved systems to be assessed, upgraded or replaced, and the cost falls on whoever owns the property when the notice lands. Either the vendor regularises it before settlement, or the price reflects a new system.
How much does a failing system cost to fix?
Repairs to baffles, lids or pumps can be under a couple of thousand dollars, but failed absorption trenches usually mean new trenches or a new system — commonly $15,000–$30,000 installed depending on soil and system type. See our cost guides for detail.
Does the septic approval transfer to me automatically?
Not always. In much of NSW the new owner must apply for (or transfer) the approval to operate, often within three months of purchase, with a fee. In other states the approval attaches to the property, but you should still confirm it's current and matches the system installed.