Vehicle and machinery wash down areas

It's important to understand the specific guidelines for the disposal of trade waste from vehicle and machinery wash down areas in your business.

A vehicle and machinery wash down area is a facility associated with car detailers, stock transport, cars, buses, trains or other forms of transport and is not available to the public for the washing of motor vehicles.

Wash down areas associated with boat, stock transporters, buses, trains, mining machinery or other forms of transport may require pre-treatment and metering installed. These businesses may also be subject to quality and quantity charges.

For information about vehicle washing associated with the car wash industry please refer to Car washes.


All businesses that intend to install or have a wash down area which is or will be connected to sewer are required to apply for approval to discharge trade waste.

The wastewater discharging to sewer must comply with our criteria:

Acceptance criteria for trade waste

Typical drawing HX33-12-20 – external mechanical wash down areas with silt sump

  • Wastewater generated from any wash down area will be required to discharge to a pre-treatment fixture. All pre-treatment fixtures used must be accepted for use within our operating areas.
  • Sites must have an accepted oil water separator such as a vertical gravity separator (VGS), coalescing plate Separator (CPS), hydro cyclone or other pre-treatment fixture that is accepted for use for the waste being discharged.
  • CPS, VGS and hydro cyclone units must have a written maintenance contract for servicing in line with the manufacturer’s requirements.
  • Single, double or triple interceptors will not be accepted as the final pre-treatment before discharge to sewer.
  • Where the wash down process is limited to cleaning of road grime from the exterior of cars, and the concentrations of total petroleum hydrocarbons (TPH) and of benzene, toluene, ethylbenzene and xylene (BTEX) in the wastewater are within the acceptable limits in IWPUB06, a solids arrestor of an accepted type is appropriate pre-treatment.
  • Only quick breakdown detergents are to be used.
  • Wash down areas are to have a bund or be designed in such a way as to prevent excess rainwater entering the sewerage system. Areas adjacent to the wash down are to be graded away from the wash bay.
  • Unroofed wash down areas are not to be greater than 20m2. Areas larger than 20m2 are required to be roofed. In exceptional circumstances this requirement may be waived, but conditions will apply.
  • All open areas which are unroofed will attract a charge based on m2 of the unroofed catchment unless their discharge to sewer is through a flowmeter.

Businesses subject to quality and quantity charges must provide flow metering and monitoring points, which must comply with the specifications outlined in: 

Trade waste flow metering

Typical drawing HX33-20-00 – trade waste monitoring points

Mains water supplies serving the wash down bays are required to have appropriate backflow prevention devices fitted. A vehicle and machinery wash down bay is deemed to be a high hazard backflow risk and therefore a boundary containment device is required to comply with our Backflow prevention policy.

All associated plumbing work must comply with Water Services Licensing (Plumbers Licensing and Plumbing Standards) Regulations 2000, AS/NZS 3500.1:2003 and AS/NZS 3500.2:2003.

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