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Plumbing in factory-built homes

From Modular Living Australia — the independent knowledge base Last updated: 22 Oct 2026

Plumbing built into a module in a factory reaches an Australian site by one of two routes agreed nationally in 2016: the whole module is certified as a WaterMark product, or its plumbing is treated as regulated plumbing work by a licensed plumber under the rules of the state where the home will stand.^[1] Either way, a licensed plumber connects it on site.^[1] Victoria, Western Australia and Tasmania publish how this works in their jurisdictions; for the other states and territories, regulator guidance specific to factory plumbing is not covered by the sources compiled here.^[3][4][5]

In a modular home, the pipes behind a bathroom, kitchen or laundry are usually installed and closed in before the module leaves the factory. By the time it is on site, a plumbing inspector sees finished linings and exposed fixtures. The question this page answers is who stands behind the plumbing nobody on site can see, and what changes when the factory is in another state or another country. Kitchen and bathroom fit-out more generally is covered in kitchens in modular homes and bathroom pods and factory-built bathrooms.

The two national routes §

In October 2016 the board that runs the WaterMark scheme decided that a prefabricated bathroom module is accepted in every Australian plumbing jurisdiction under one of two routes, and that similar modules such as prefabricated kitchen modules are treated the same way.^[1]

Route 1 — the module is a certified product

The whole module is certified to the relevant WaterMark specification. The certifier records which certified components are built into it, any substitution has to be notified and evaluated, and the licence holder declares each year that the module still conforms.^[1] It may be made in Australia or overseas.^[6] A licensed plumber installs it on site.^[1]

Route 2 — the plumbing is regulated work

The plumbing is treated as ordinary plumbing work, done in the jurisdiction that has authority over the site. A licensed plumber does or approves the joining of components, the components themselves carry WaterMark certification where it is required, and a licensed plumber installs the finished module. The module as a whole does not need to be WaterMark certified.^[1]

Anyone planning to use the second route is expected to check the requirements of the local plumbing authority first.^[1] The specification used for the first route, WMTS-050, covers shower, bathroom, laundry and kitchen modules and combinations of them; a module with no built-in plumbing components, relying on standard fittings connected on site, does not need certification under it.^[2]

What a certified module carries §

A module certified under WMTS-050 has to be permanently marked with the manufacturer's name or brand, the WaterMark logo and licence number, its maximum operating temperature and pressure, its flow rates and the specification number.^[2] Every unit is pressure tested before release, and the manufacturer supplies installation, operating and maintenance instructions.^[2]

The certificate has a clear limit. A WaterMark licence for a bathroom pod covers the Plumbing Code of Australia only; it does not certify the pod's structure, electrical work, waterproofing or fire protection, which need their own evidence of compliance.^[6] A WaterMark logo on a pod is therefore not evidence that the shower will not leak into the floor beneath it. Waterproofing rules for bathrooms are set out in bathroom pods and factory-built bathrooms, and WaterMark for individual products in imported prefab compliance.

Built in another state or overseas §

This is where the two routes stop being interchangeable. The ABCB's handbook states that a pod made interstate or imported needs only to meet the WaterMark product requirements, and that a state is not obliged to accept regulated plumbing work carried out in another state.^[6]

The published state positions follow from that:

• Victoria treats any plumbing system built outside the state as a plumbing product, because its Building Act applies only in Victoria; it needs evidence of suitability before installation.^[3]
• Western Australia allows the regulated-work route only for work done in WA; the WaterMark route can be used anywhere, in Australia or overseas.^[4]
• Tasmania encourages interstate manufacturers to have their plumbers obtain a Tasmanian licence, to avoid delays when the work is assessed.^[5]

For a buyer, the practical point is to ask, before the contract is signed, where the module will be built and which route its plumbing will follow. A factory interstate or overseas relying on its own local plumbing sign-off may not satisfy the state where the home will stand. Buying a home built overseas is covered in buying an imported prefab home.

State by state §

Victoria

The Victorian regulator's guidance, published in 2016 under its former name, the Victorian Building Authority, requires the builder of an off-site plumbing system to choose one method at the start:^[3]

• As plumbing work, available only where the work is done in Victoria: a registered or licensed plumbing practitioner does the work to the prescribed standards and issues a compliance certificate.
• As a plumbing product: the system needs evidence of suitability, primarily a WaterMark certificate of conformity, or for a product outside the WaterMark scheme other evidence such as a report from a registered testing authority or a professional engineer's certificate.

Under either method, installation and commissioning on site must be done by a registered or licensed practitioner and a compliance certificate issued. Where one plumber builds the system and another installs it, each issues a certificate for their own work.^[3] Whether Victorian requirements have changed since the 2016 fact sheet is not covered by the sources compiled here; the regulator now operates as the Building and Plumbing Commission.

Western Australia

Since 10 February 2025, Western Australia has had specific rules for modular plumbing work: water supply or sanitary plumbing done while building a plumbing module.^[4] The definition is broad. Its examples include bathroom modules, prefabricated walls with built-in plumbing, kitchen and laundry modules, mining accommodation and transportable buildings.^[4]

The work can be done in one of two ways. Under the regulations, it is carried out by or under a WA licensed plumbing contractor, who certifies it like other major plumbing work, and only in WA. Alternatively, the manufacturer certifies the module under WMTS-050.^[4] Either way, the module must be certified before it is connected to plumbing or drainage on site, and the state recommends a data plate on the module showing the contractor's licence number and Certificate of Compliance number.^[4] Transportable home rules in WA covers the wider approvals.

Tasmania

Tasmania's plumbing regulator distinguishes three cases.^[5]

• A prefabricated building for a permanent site goes through the full plumbing approvals process. Plumbing work cannot start until a Certificate of Likely Compliance has been issued and the start of work authorised, and the council must be notified before work is concealed so it can inspect or authorise the work to continue. The permit authority decides what evidence it accepts, which may include photos, inspections, the manufacturer's quality assurance reports and pressure testing of drains and water services after delivery.
• An unregistrable relocatable building — designed to move between sites, such as a site shed — carries a compliance plate.
• A WaterMark-certified module made to WMTS-050 is accepted in all Australian plumbing jurisdictions and is connected, tested and certified on site by a licensed plumber.

The modular approvals process in Tasmania more broadly is covered in modular home rules in Tasmania.

New South Wales

In August 2024, Building Commission NSW described the position at that date: a prefabricated plumbing system arriving on site was treated as a product, so regulated plumbing work was limited to what the installer did on site, and factory work outside NSW needed no NSW licence.^[7] The same paper reported that audits of NSW apartment buildings with bathroom pods had found non-compliant plumbing fixtures, non-compliant waterproofing and unsafe electrical wiring.^[7] The paper set out proposals and stated that it did not reflect final government decisions.^[7]

NSW has since passed legislation on prefabricated buildings that is not yet in force; it is covered in NSW building law reform 2026. How factory plumbing will be treated once that legislation commences is not covered by the sources compiled here.

Queensland, South Australia, ACT and Northern Territory

The Queensland regulator's published requirements divide plumbing into permit, notifiable and minor work, all carried out by a QBCC licensee, but do not address plumbing built off site.^[8] For Queensland, South Australia, the ACT and the Northern Territory, regulator guidance specific to factory plumbing is not covered by the sources compiled here. The national decision that a bathroom module is accepted in every plumbing jurisdiction under one of the two routes still applies.^[1]

Summary §

Common questions §

Does a factory-built bathroom need a WaterMark?

Not always. Nationally, a bathroom module is accepted either as a WaterMark-certified product or as regulated plumbing work by a licensed plumber in the state where the home will stand; under the second route the module as a whole does not need WaterMark certification, though components that require it still do.^[1]

Can a factory in another state sign off the plumbing?

Not necessarily. The ABCB states that a state is not obliged to accept regulated plumbing work done in another state, and that an interstate or imported pod needs to meet WaterMark product requirements.^[6] Victoria treats systems built outside the state as products.^[3]

Does a WaterMark on a bathroom pod cover the waterproofing?

No. A WaterMark licence for a pod covers Plumbing Code requirements only, not waterproofing, structure, electrical work or fire protection.^[6]

Who connects a module's plumbing on site?

A licensed plumber, under both national routes.^[1] In Victoria the on-site installation and commissioning also needs a compliance certificate.^[3]

Do the same rules apply to kitchens and laundries?

Yes. The national decision extends to similar modules such as kitchen modules, and the WaterMark specification covers bathroom, shower, laundry and kitchen modules.^[1][2]

What is not covered here §

Regulator guidance on factory plumbing in Queensland, South Australia, the ACT and the Northern Territory is not covered by the sources compiled here, and neither is any change to Victoria's requirements since its 2016 fact sheet. How the NSW prefabricated building legislation will treat factory plumbing once in force is not covered.

Electrical work and gas fitting carried out in a factory are regulated separately; electrical work is covered in electrical work in factory-built homes, and gas fitting is not covered. Plumbing fees, compliance certificate thresholds and inspection charges are not covered.

No source compiled here reports how often factory plumbing fails compared with plumbing installed on site.

Questions worth asking §

• Where will the module be built — in this state, another state or overseas?
• Will the plumbing be a WaterMark-certified module, or regulated plumbing work by a plumber licensed in this state?
• If it is WaterMark certified, what is the licence number, and does it appear on the module?
• Who will issue the plumbing certificates for the factory work and for the connection on site?
• What evidence will the permit authority or certifier accept for plumbing concealed in the factory, such as photos, inspections or pressure tests?
• What separate evidence covers the waterproofing and electrical work in the bathroom and kitchen?

Related: electrical work in factory-built homes · service connections · handover inspections on a modular home · inside a prefab factory

References §