Rainwater Tank Plumbing Requirements and Connection to Mains

What This Requirement Covers

This requirement sets out the plumbing, backflow prevention and installation standards for rainwater storage tanks and any direct or indirect connection between a rainwater system and a reticulated (mains) drinking water supply in Australia. It exists to protect public drinking water from contamination (microbial, chemical and particulate) that can arise when non-potable sources such as roof-harvested rainwater are connected to potable distribution systems, and to ensure tanks and associated pipework are fit-for-purpose, accessible and maintainable.

The rules apply to designers, builders, plumbers and property owners who install, modify or connect rainwater tanks on residential and commercial sites. They cover tank construction and materials, identification of non-drinking water services, device selection and installation for containment/zone/point-of-use backflow protection, and testing and certification requirements referenced in the Plumbing Code of Australia (NCC 2022 Volume Three) and the relevant Australian Standards.

Key Requirements

1. Tanks and materials
2. Tanks must be selected from relevant standards and materials in contact with drinking water must comply with AS/NZS 4020, as specified in NCC 2022 Volume Three, Section B (see Part B references and the Water services section). Plastic tanks must comply with AS/NZS 4766 (NCC 2022 Volume Three, Section B).
3. Identification
4. Rainwater storage that is not intended for potable supply must be identified as rainwater in accordance with AS/NZS 3500.1, as specified in NCC 2022 Volume Three (see Section B and VIC B7D3).
5. Connection and protection levels
6. Connection of any rainwater system to a drinking water service must comply with backflow protection requirements in AS/NZS 3500.1 (2018) Clause 16.4 and Table 16.4, and the Plumbing Code of Australia provisions in NCC 2022 Volume Three, Part B (B5D6/B5D4/B5D5).
7. Backflow protection must be provided appropriate to the hazard rating of the connection: typical protection methods include containment, zone protection and point-of-use protection using devices selected and installed in accordance with Section 4 of AS/NZS 3500.1.
8. Specific device notes and performance
9. Devices used for containment or zone protection must be suitable and, where required, testable (for example testable reduced pressure zone devices) in line with AS/NZS 3500.1 and NCC Volume Three guidance (see B5D4, B5D6).
10. In some low-risk buried or partially buried tank scenarios a dual-check valve may be permitted instead of a testable device following risk assessment and subject to state amendments (for example South Australian requirements in NCC Volume Three, SA provisions referencing clause 16.4.2).
11. Installation references
12. Connection and installation of cold-water storage tanks used to supply a drinking water service must comply with NCC 2022 Volume Three B1D7 and sections 8 and 15 of AS/NZS 3500.1 (NCC Volume Three text).
13. Materials and potable contact
14. All linings, sealants and products that contact potable water must comply with AS/NZS 4020 and be WaterMark certified where required (NCC 2022 Volume Three, Section B references).
15. Testing and certification
16. Backflow prevention devices and installations must be installed, commissioned and, where required, tested in accordance with AS/NZS 3500.1 and relevant state plumbing legislation; test certificates or evidence of commissioning may be required by the relevant authority.
17. Measurement and values to consider (common thresholds and metrics referenced in standards and NCC)
18. Pressure class and device selection: follow AS/NZS 3500.1 device pressure ratings and selection tables (device working pressures often specified in kPa in the device standard or manufacturer documentation).
19. Tank standards: plastic tanks to AS/NZS 4766; product contact testing to AS/NZS 4020.

Residential vs Commercial

1. Residential (Class 1 and 10)
2. The same fundamental backflow protection hierarchy in AS/NZS 3500.1 and NCC Volume Three applies. For a typical single dwelling where rainwater is used for toilet flushing, laundry or irrigation, designers commonly use zone protection (e.g. an approved backflow prevention device at the point the rainwater system interfaces with potable distribution) or containment (an appropriately tested device at the service head) depending on the arrangement. Identification of non-potable lines and correct labelling is required per AS/NZS 3500.1 and NCC Volume Three (B7D3).
3. Domestic tanks installed to supply a drinking water service (for example as an alternative potable source) must meet the requirements of B1D7 and AS/NZS 3500.1 sections referenced in NCC Volume Three.
4. Commercial (Class 2-9)
5. Commercial and multi-unit buildings generally face stricter application of containment protection and device testing due to higher hazard risk and more complex pipework. Fire-fighting water services, recycled water or other non-drinking supplies must be isolated from the potable service by an appropriate backflow device selected and installed in accordance with Section 4 of AS/NZS 3500.1, and additional NCC clauses such as B5D4 apply for fire services.
6. Mixed-use or multi-occupancy sites may require more robust containment (testable devices), routine testing regimes and compliance evidence to the authority, per NCC 2022 Volume Three and state plumbing regulation.

Exceptions and Exemptions

1. Risk-assessed alternatives
2. Where a risk assessment demonstrates low risk to drinking water quality, some jurisdictions permit alternatives to testable containment devices. For example, South Australia’s variation in NCC Volume Three allows a dual-check valve for containment/zone protection for certain buried or partially buried tanks when a documented risk assessment supports that decision and the authority accepts it (see NCC 2022 Volume Three - SA provisions and clause 16.4.2).
3. Drinking water supply from rainwater
4. Where rainwater storage is intended and installed to supply potable uses, identification of storage and holding tanks as non-potable is not required (see VIC B7D3 in NCC Volume Three). However, potable use imposes full compliance with materials, hygiene and AS/NZS 4020 testing and the relevant sections of AS/NZS 3500.1.
5. Local exemptions
6. Some minor installations or isolated, non-connected tanks may be outside the scope of certain containment requirements; however, state plumbing regulation and local water authority rules determine exemptions. Always check the local authority.

State and Territory Variations

1. General note: NCC 2022 Volume Three is the national Plumbing Code of Australia, but states and territories include schedules and variations that modify or add requirements. Always verify against your jurisdiction’s schedule in NCC 2022 Volume Three (Schedules 4-12) and local plumbing legislation.
2. South Australia
3. SA inserts clause 16.4.2 allowing, after suitable risk assessment, the use of a dual-check valve in lieu of a testable device for certain buried or partially buried tanks without a drinking water connection or with direct/indirect connections, subject to specified design and installation precautions and submission to the authority (NCC 2022 Volume Three, SA provisions).
4. Victoria
5. Victoria requires identification of rainwater storage as rainwater in accordance with AS/NZS 3500.1, unless the rainwater is intended for drinking and personal hygiene (see NCC 2022 Volume Three, VIC B7D3).
6. Other jurisdictions
7. The NCC text includes B5D6 and related clauses for protection of drinking water services from rainwater, and many states reference AS/NZS 3500.1 Clause 16.4 and Table 16.4 directly. Local water authorities and state plumbing regulations may add testing/documentation, device certification or additional containment requirements (e.g., device types accepted, periodic testing intervals). Consult the relevant state schedule in NCC 2022 Volume Three and local plumbing authority for precise amendments.

Practical Compliance Tips

1. Follow AS/NZS 3500.1 Clause 16.4 and Table 16.4 for selecting the correct backflow protection level - containment where practicable for any connection to a drinking water service.
2. Label all non-potable lines and tanks clearly and permanently in accordance with AS/NZS 3500.1 and NCC Volume Three identification requirements to avoid accidental cross-connections.
3. Use WaterMark certified products and ensure materials in contact with potable water comply with AS/NZS 4020; obtain manufacturer evidence and include it in the compliance file.
4. Where a risk assessment is relied on (for example to use a dual-check device in SA), document the assessment thoroughly, include design and maintenance controls (filters, first-flush diverters, overflow reflux valves, mosquito screens), and submit to the authority where required.
5. Install testable backflow devices where the NCC or local authority requires testable containment or zone protection; schedule routine testing and retain test reports as part of the building/plumbing compliance records.
6. For potable use of rainwater, ensure tanks, linings and fittings meet AS/NZS 4020 and tank construction standards such as AS/NZS 4766 for polyethylene tanks, and follow AS/NZS 3500.1 installation sections 8 and 15 for cold-water storage tanks.
7. Check state schedules and local water authority technical requirements early in design - device types accepted, certification, labelling, inspection/test intervals and any permitted alternatives vary by jurisdiction and will affect specification and costs.

Sources: NCC 2022 Volume Three - Plumbing Code of Australia (Part B water services, clauses B5D4, B5D6, B1D7, VIC and SA variations), AS/NZS 3500.1 (Water services) Clause 16.4 and Table 16.4, AS/NZS 4020, AS/NZS 4766.

Could not provide clause page numbers beyond the document references above; always verify the current NCC and state schedules before construction or certification.