Greywater recycling

Greywater is wastewater from bathrooms, diverted for garden irrigation or (if the greywater is treated) for toilet flushing.

On this page:

  • Code requirements
  • Safety considerations

Greywater is water from basins, baths and showers. It can be recycled for use in garden irrigation and, if treated, for toilet flushing. Recycling greywater:

  • reduces the load on sewerage systems including on-site treatment systems
  • provides a garden water supply, reducing demand on other sources of water

Code requirements

Any on-site wastewater treatment system must meet performance requirements for construction and operation of the Building Code. If the system is designed to AS/NZS 1547 On-site domestic-wastewater management, the requirements of the Code will be met.

Some local authorities in New Zealand encourage greywater recycling, but other authorities do not. The local authority should be contacted before you begin to design a system.

The sanitary plumbing connected to an on-site wastewater treatment system within the house must comply with the requirements of NZBC clause G13 Foul water.

Safety considerations

Greywater recycling must be designed and installed with care as it is potentially unsafe in some situations. To reduce risk, greywater used for garden irrigation should deliver water below the soil surface.

The Ministry of Health considers that greywater recycling carries potential health risks and does not support it in homes.

BRANZ does not recommend greywater use for:

  • washing clothes
  • garden irrigation by sprinkler
  • use on vegetables or salad plants.

Collected rainwater is a preferred option for toilet flushing than greywater.
Greywater systems must be designed so that any overflow can be discharged to a sewer or on-site blackwater treatment system.

Laundry water may also be classified as greywater but, as it may contain detergents and other contaminants, BRANZ does not encourage its recycling.