Water

Water use, sustainability, and efficiency by choosing quality systems and materials, and providing environmentally friendly solutions.

Greywater recycling

Greywater is wastewater from baths, showers and hand basins (and in some cases, from laundries) that is reused for irrigation or, with appropriate treatment, toilet flushing.

On this page:

  • Code requirements
  • Safety considerations

AS/NZS 1547:2012 On-site domestic-wastewater management defines greywater as “the domestic wastes from a bath, shower, basin, laundry and kitchen, but excluding toilet and urinal wastes.” However, some people prefer not to reuse wastewater from clothes washing machines because of the enzymes, detergents and other chemicals in it. Some systems do not reuse kitchen wastewater because it contains fats and other organic matter (especially if there is a food disposal unit in the sink). Kitchen wastewater also has the potential to carry contamination from organisms such as Campylobacter that come from preparing raw meat for cooking.

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.

While recycling greywater has benefits, maintenance – in particular, cleaning or replacing filters – is required to keep these recycling systems operating properly. Specific maintenance tasks should be pointed out to clients considering this option, without discouraging them, before they make a final decision.

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, 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. Proprietary systems are available in the New Zealand market. To reduce risk, greywater used for garden irrigation should deliver water below the soil surface.

Public health authorities in New Zealand typically do not support the use of greywater.

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. Where greywater is used for toilet flushing it should be filtered, treated to remove odours and disinfected. The water is likely to be cloudy.

A greywater system should have a bypass switch so that the greywater can be sent directly into the sewer or on-site blackwater treatment system if there is something in it that house occupants do not want to go into the garden. Water with faecal matter from bathing very small children should be diverted, for example. There should also be provision for overflow to be discharged to a sewer or on-site blackwater treatment system.

Some proprietary systems have a sensor that diverts greywater if there is already enough water in the garden.

 

Updated: 23 January 2018