Greywater is household wastewater from laundry tubs, washing machines, showers, baths and basins. Kitchen sinks and dishwashers are included under the term “greywater” but tend to contain higher levels of contaminants than other greywater sources. Changing domestic lifestyles are driving an increase in water use, creating a need for sustainable options for reuse or disposal of the resulting wastewater.

Many regional and district councils are now considering alternative water management strategies, including rainwater collection and greywater diversion. However, no national legislation or guidelines currently exist for rainwater or greywater practices, and there is a lack of health risk assessment data specific to New Zealand conditions. Given the prevalence of unreported greywater re-use, the CIBR's greywater experts believe research needs to be conducted to address this. A CIBR report exploring the drivers for greywater reuse in New Zealand can be found here.

CIBR's “Greywater-wise” programme was led by ESR. Please feel free to contact ESR if you would like to discuss this research ( 

Greywater-wise projects

Septic tanks and greywater. The impact of greywater re-use on the efficiency of a septic tank system was investigated by studying two domestic properties – one with a well-functioning septic tank system, and one with a poorly functioning system. The full report was published in the Water Journal (Water NZ) Issue 178.

Triclosan in greywater. A study by MSc student Morkel Zaayman, looking at the environmental impacts of triclosan – an antimicrobial found in personal care products such as toothpaste and mouthwash, and therefore greywater. Morkels thesis can be found here (external link) .

Long term unregulated greywater disposal. Unclear regulations and/or guidelines have resulted in extensive unregulated greywater disposal. We used a community where long term greywater disposal was common as a case study for this project. Soil that had been exposed to greywater for up to 20 years was analysed and compared with a nearby control soil. The published paper can be found here (external link) .

Microbial survival in mulch. This project investigated the survival of the indicator organism Escherichia coli in different mulch types that may be used to cover an area that is sub-surface irrigated with greywater. This data has not yet been published – please contact ESR directly for further information.