Third pipe schemes
A third pipe scheme provides non-drinking water to multiple users as an additional water service to the mains scheme that supplies drinking water and the sewerage scheme that takes used water away from the house.
Plumbing design standards apply to avoid cross-contamination with the drinking water supply, and a dedicated set of purple-coloured pipes are required to avoid confusion and risks to public health.
Third pipe schemes require a water service provider and, depending on the scale of the operation, the provider will require either a licence to operate the scheme under the Water Services Licensing Act 1995 or need to apply for an exemption from licensing. Proponents should seek advice from the Water Services branch of the Department of Water on their particular scheme.
The best opportunity for the installation of third pipe schemes is in new residential developments, where the pipeline can be constructed at the same time as other underground infrastructure.
Brighton Estate north of Perth is an example of an operational third pipe scheme in Perth, with the Water Corporation as the service provider. It provides groundwater from a community bore for irrigation of household gardens and public parks.
Third pipe scheme infrastructure standards
Distribution systems (including all pipe work, fittings and drainage of the water) should be designed to comply with Australian Standards; ensure the separation and prevention of cross connection between non-drinking water and drinking water schemes; and where a recycled water scheme is proposed it should comply with the Department of Health Guidelines for the non-potable uses of recycled water in Western Australia (August 2011).
The requirements of the WSAA national standards for dual reticulation schemes are listed in Dual Water Supply Systems (First Edition, Version 1.2) A Supplement to the Water Supply Code of Australia WSA 02-2002 (November 2005). This guideline covers the design and construction of dual water supply systems for servicing new developments and can be downloaded free-of-charge from the WSAA website.
Requirements for the drinking water part of a dual water supply scheme should be in accordance with the Water Services Association of Australia (WSAA) Water Supply Code of Australia WS 03 and with Water Corporation's supplementary requirements.
Within a property, third pipe schemes should be designed, installed, identified and maintained to prevent cross-connection with a drinking water service. This risk is addressed through the AS/NZS 3500:2003 National Plumbing and Drainage Code and the Plumbing Regulations 1998. These regulations set out the standards of work for water services from the supply source to the point of discharge and the requirements for the selection and installation of back flow prevention devices. As best practice, only a licensed plumber should work on any part of a non-drinking water connection.