Recycled Water in Residential Plumbing: Purple Pipe Systems

What it is

Recycled water in a residential context is highly treated wastewater delivered through a second reticulated network running alongside the drinking water network. The two networks are physically separate, separately metered and identified by colour so they cannot be confused. The system is known as dual reticulation or, less formally, a purple pipe scheme.

Recycled water is used for non-drinking purposes such as toilet flushing, garden watering, washing machine cold feed (in some authorities), car washing and outdoor cleaning. It is not for drinking, cooking, bathing, food preparation or pet drinking water.

Where purple pipe is used

Dual reticulation networks are common in newer suburban estates in Sydney (Rouse Hill, Pitt Town), south-east Queensland, parts of Melbourne (Werribee, Aurora) and several South Australian and Western Australian developments. Each scheme is operated by a water authority and a property is connected to either the network or it is not. A homeowner cannot opt out of recycled water if their estate is built around it.

Class A recycled water

Class A is the highest treatment grade used for residential dual reticulation. It is treated to a level that makes accidental contact with skin acceptable, although it is still not safe to drink. Other classes (B, C, D) exist for agricultural and industrial reuse with lower treatment grades and stricter access controls.

Identification under AS/NZS 3500.1

AS/NZS 3500.1 sets the rules for how recycled water pipework, fittings and outlets are identified so that a plumber, occupant or contractor cannot mistake them for drinking water.

Pipe colour

All recycled water pipework above and below ground must be coloured purple (also described as lilac). The purple colour applies to the body of the pipe or to a continuous purple stripe along its length.

Buried pipe marking

Below-ground recycled water pipes must be marked with purple identification tape laid above the pipe in the trench. This warns anyone excavating in the future that the pipe is recycled water and not drinking water.

Tap and outlet identification

Every recycled water tap must be marked with a permanent warning that reads "Recycled water Do not drink" or equivalent wording. Tap handles in dual reticulation systems are typically supplied with a lockable, removable key handle on outdoor taps to discourage accidental drinking water use.

Signage requirements

Signage at recycled water outlets, garden taps and pump points uses standardised wording and pictograms drawn from AS 1319 Safety signs for the occupational environment. The "Do not drink" pictogram (a crossed-out drinking glass) is the universal symbol used at all recycled water outlets.

Signage cannot be removed, painted over or obscured. Any plumber who removes a sign without replacing it commits a plumbing offence in most jurisdictions.

Cross-connection prevention

The biggest risk in a recycled water property is a cross-connection, where the drinking water and recycled water pipes are accidentally joined. This can happen if a plumber installs a new fixture and connects it to the wrong line, or if a homeowner extends an outdoor tap.

Boundary backflow

Properties on a recycled water scheme are treated as a high hazard for backflow purposes. A high hazard containment device is fitted on the drinking water meter. This protects the street drinking water main if a cross-connection occurs inside the property.

Audit and commissioning

Before a new recycled water property is connected, the water authority requires an inspection that confirms the recycled and drinking water systems are physically separate. A pressure test isolates each network and confirms no flow between them. The plumber and the water authority both sign off before the meter is set live.

Renovations and extensions

Any plumbing work inside a recycled water property must be done by a licensed plumber who is briefed on dual reticulation. The two networks must remain physically separate at every fitting. After the work is complete a re-test of separation is often required, depending on the scope.

Where the rules sit

The primary technical requirement comes from AS/NZS 3500.1 Water services, called up by NCC Volume Three. State-level requirements are set by each water authority and by the relevant plumbing regulator. Signage uses AS 1319 conventions. Class A treatment standards are governed by state public health guidelines (for example the Victorian Class A recycled water guidelines published by the Department of Health).

A plumber working on a dual reticulation property who does not separate the networks faces fines, plumbing licence action and personal liability for any public health harm that follows. The cost of a cross-connection event includes mains flushing, disinfection and public notification, which water authorities recover from the responsible party.