PERTHSewer connection and drainage: where your responsibility runs to
WA sewer connection rules: drainage plumbing runs to the main sewer junction (IB 163), the 1 July 2024 PLB certification, AS/NZS 3500.2
The drain that carries waste from your house to the public sewer is your responsibility, all the way to where it meets the main, and the rules on who can work on it tightened in 2024. If you are buying a home, or planning drainage work, it is worth knowing where your responsibility begins and what paperwork should exist.
Where your responsibility runs to
People assume the water authority owns the sewer the moment it leaves the house. It does not. Building and Energy's Industry Bulletin 163 clarified that drainage plumbing includes the property sewer connection all the way to the junction on the main sewer. That connecting length, running from your fixtures out to the public main, is drainage plumbing, and it is on the property side of the line for the work and its compliance.
The 2024 change: who can do it, and the certification
From 1 July 2024, this work must be carried out under the supervision of a licensed plumbing contractor and certified with the Plumbers Licensing Board. Until recently that certification was not required; the change came out of consultation between the Water Corporation and the Plumbers Licensing Board.
The certification is not a single form. It involves a notice of intention before the work, notification when the drainage work is completed, a certificate of compliance, and a drainage plumbing diagram, a record of where the drainage actually runs on the property. That diagram is the part that outlasts everyone: homeowners, plumbers and future buyers all use it to work out the layout of the drainage under a property, which is otherwise invisible and expensive to guess at.
The standard behind it
Sanitary plumbing and drainage is governed by AS/NZS 3500.2, the Australian standard for sanitary plumbing and drainage, which sits within the Plumbing Code of Australia. It sets the technical requirements, pipe grades, venting, connections, that a compliant drainage system has to meet, and it is why this is licensed work rather than something an owner should attempt on the sewer side.
Why it matters to a buyer
Drainage problems are among the most disruptive and expensive a home can have, because the pipes are underground and a failure is not visible until it backs up or the ground gives way over a collapsed line. Two things are worth knowing on a purchase.
First, whether a drainage plumbing diagram exists for the property. It tells you where the drains run, which matters if you plan to build, landscape or add a pool — digging blindly into an unmapped sewer line is a costly mistake. Second, tree roots. In older Perth suburbs with large street trees and ageing clay drainage, root intrusion into sewer lines is common, and it is one of the things a plumber's drain camera finds that no visual inspection can.
A pre-purchase inspection under AS 4349.1 does not include the concealed drainage — that is licensed plumbing work outside the inspection's scope — but it reports the visible signs that point to a drainage problem, and recommends a plumber's drain inspection where the evidence warrants it. On an older home with mature trees, that camera inspection is often money well spent before you buy.
The boundary that decides who pays
The single most useful thing to understand about sewer and drainage is where your responsibility ends and the water authority's begins, because that boundary decides who pays when something goes wrong, and it catches people out constantly. In broad terms, the property owner is responsible for the drainage within their own land, the pipes that carry waste from the house to the connection point, while the authority is responsible for the main sewer that the connection runs into. The exact point of the boundary, and the rules around it, are not something to guess at, because a blockage or a collapse on your side of the line is your bill, and one on the authority's side is theirs.
For a buyer, this matters because drainage problems are both common and expensive, and they are almost entirely invisible during an ordinary inspection. A partially collapsed or root-invaded drain on the owner's side of the boundary can cost a great deal to put right, involving excavation or relining, and none of it is apparent from walking through the house. This is one of the areas where knowing the limits of a standard inspection is important: the visible plumbing fixtures can be checked, but the buried drainage between the house and the connection is not something a visual inspection sees, and where there is reason for concern, a specialist drain inspection with a camera is the tool that actually answers the question.
Why older suburbs carry more drainage risk
The age of the property and the suburb tells you a lot about the likely state of the drainage. In Perth's older established suburbs, the drainage may be decades old, and the materials and methods of earlier eras, earthenware pipes with mortar joints, for instance, are far more vulnerable to root intrusion and to the movement of reactive soils than modern PVC. Large established trees, which are one of the attractions of the older suburbs, are also the main threat to old drains: roots find the smallest gap at a joint, work their way in seeking the water and nutrients, and gradually block or fracture the pipe. A house with beautiful mature trees and original earthenware drains is a house where the drainage deserves thought.
Newer homes are not immune, but the risk profile is different. On reactive clay sites, ground movement can stress and crack drainage over time regardless of the pipe material, and on any site poor installation, drains laid to inadequate falls or badly jointed, produces problems that show up years later as recurring blockages. The point for a buyer is that drainage risk is real, largely hidden, and correlated with age, soil, and trees, which are exactly the things you can see about a property even though the drains themselves you cannot.
What a buyer should actually do about it
Given that the drainage is buried and potentially expensive, the sensible approach is proportionate to the signals. On a newer home on stable ground with no history of problems, the drainage is a low concern and the visible plumbing check is usually enough. On an older home in an established suburb, particularly one with large trees, a history of blockages, or any sign of drainage trouble like slow-draining fixtures or gurgling, a dedicated CCTV drain inspection is worth commissioning before you commit, because it is the only way to actually see the condition of the pipes rather than guessing. It is separate, specialist work, and a building inspection report will say where it is warranted rather than pretending to have assessed something it cannot see. Spending a modest amount to camera the drains before settlement is cheap against discovering a collapsed drain under an established garden afterwards, when the cost and the disruption are both yours.
The blind spot to keep in mind
The theme that runs through everything about sewer and drainage is that it is largely a blind spot in an ordinary property purchase, and keeping that in mind is what protects a buyer. The drainage is buried, it can be expensive to repair, the responsibility boundary decides who pays, and none of it is visible in a walk through the house or in a standard building inspection. A clean building report is not a clean bill of health for the drainage, because the two are simply different assessments looking at different things. On a newer property on stable ground this is a low concern. On an older one, in an established suburb, with mature trees or any symptom of drainage trouble, it is worth the modest cost of a camera inspection to see the drains for what they are, before settlement rather than after, because afterwards both the bill and the disruption are yours alone.
Common questions
Who is responsible for the sewer connection?
The property owner. Industry Bulletin 163 clarified that drainage plumbing includes the property sewer connection all the way to the junction on the main sewer — that length is on the property side.
Who can do sewer connection work in WA?
From 1 July 2024, it must be done under a licensed plumbing contractor and certified with the Plumbers Licensing Board, including a notice of intention, completion notification, certificate of compliance and a drainage plumbing diagram.
Should I get a drain inspection when buying?
On an older home with mature trees, often yes. Root intrusion and pipe deterioration are common in older Perth drainage, and a plumber's drain camera finds what a visual building inspection cannot.
This comes up on every pre-purchase building inspection and building & timber pest inspection we carry out.
Read next: the little grille in the brickwork is doing a job and drainage plumbing diagram: the map of your underground drains.
Sources
Read rather than recalled. Summarised here; the documents themselves are Crown copyright and are linked rather than reproduced.