Water

Greywater is wastewater from baths, showers, hand basins and under some definitions laundries. It does not include human waste from toilets, although there may be small amounts of this in greywater if laundry tubs are used to rinse soiled clothing or babies’ nappies.

Kitchen wastewater must not be re-used because it contains oils, fats and other wastes that support the growth of micro-organisms and would cause blockages in a greywater distribution system. Some detergents and cleaning agents, including those used in dishwashers, are very alkaline and may damage the soil and plants. Kitchen wastewater should be discharged to a sewer or to a septic tank or other on-site blackwater treatment system.

Recycling greywater reduces the load on sewerage systems, including onsite treatment systems. Greywater can replace potable water for garden irrigation, and can be used for toilet flushing if it receives treatment to minimise growth of micro-organisms in the cistern.

Is greywater safe for re-use?

Though greywater recycling appears to be a simple concept, there are many situations in which a greywater recycling system is likely to be inappropriate and potentially unsafe.

Greywater recycling systems have been actively promoted in countries with serious water shortages. Although some New Zealand local authorities have encouraged greywater recycling, others restrict it. The Ministry of Health considers that it carries potential health risks and, for that reason, it does not support re-use of greywater within houses. BRANZ does not recommend using greywater for:

• washing clothes
• garden irrigation by sprinkler, or on vegetables or salad plants that are eaten uncooked.

Collected rainwater is a better option for toilet flushing than greywater.

The best greywater systems are those that deliver suitable water directly beneath the garden surface.

Restrictions on greywater recycling systems

Greywater recycling systems are not commonly installed in multi-unit housing (although it has been used overseas) especially where the irrigated land area is small.

Operation and maintenance

The owner must be made aware that even a well-designed greywater system, however simple or complex, requires regular attention and maintenance.

For your clients

To help your clients understand onsite wastewater treatment options, safety issues, and the importance of maintenance, refer them to www.smarterhomes.org.nz/water/on-site-sewage-systems and www.smarterhomes.org.nz/water/re-using-greywater.