Domestic Greywater Reuse: Preliminary Evaluation

This report was produced for the Urban Water Research Association of Australia, a now discontinued research program.

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Report no. UWRAA 60

July 1993

Synopsis

Residential reuse of wastewater for non potable purposes has been in practice overseas for more than a century. The economics of supplementing water supply resources and reducing wastewater discharge have been the catalyst for many of the authorities which approve the practice.

The segregation of domestic wastewater at the source into two separate flows gives “Blackwater” and “Greywater” (also referred to as sullage). Blackwater is water closet, bidet and bidette waste and thus has gross faecal contamination. Greywater is all the remaining household waste water e.g. bath, laundry etc and by definition is not deemed to be faecally contaminated. Investigations undertaken during this project indicate, however, that this is not a reliable definition as it greatly depends on practices within the home.

The project was conducted to provide an insight into the potential for on-site domestic use of greywater in Australia and included a comprehensive postal enquiry of foreign embassies and overseas environmental protection agencies, literature searches using the key word “greywater”, and enquiries to all the major water authorities within Australia. Some users of septic tank pump-out systems in the Brisbane Region were also surveyed. This report describes overseas practices, water and cost saving benefits, scientific analysis of health risks for Domestic Greywater Reuse and design criteria.

Residential reuse of greywater is not presently permitted in Australia but neither is it precluded because the terminology is not recognised. Potential risks to public health, the impact on the urban environment and the economics of greywater reuse need to be investigated before such use can be permitted.

The preliminary studies undertaken in this project indicate that the volume of greywater produced in most households is sufficient to meet all toilet flushing requirements and/or a significant portion of current outdoor usage on lawns and gardens and that, subject to the development and implementation of guidelines to protect public health and the environment, there would be no appreciable risks involved. Further studies are being undertaken to develop these guidelines.

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