The Challenge
Recent drought conditions in South Eastern Australia resulted in increasing use of alternative water sources for watering Melbourne’s domestic gardens. Greywater from bathrooms, laundries and kitchens is widely available as an alternative source that can be collected and used at little additional cost. Greywater typically contains contaminants from domestic products and may contain other contaminants as a result of inappropriate disposal practices. Greywater also contains variable levels of microbial contamination of human origin from faecal, dermal and, respiratory sources which may pose a variety of health risks.
This study was designed to characterise greywater use practices and greywater quality in Melbourne households and to assess potential health risks arising from use of greywater on home grown produce.
The Project
A survey of greywater use in a representative sample of Melbourne households, covering the prevalence, frequency and purpose of use during the period 2007 to 2011 was conducted by phone, mail and internet. Sample collection and microbial water quality testing of greywater samples from a subset of these households was undertaken. Information obtained from the survey and this sampling program was used to perform modelling of the disease burden associated with current greywater usage practices using the Quantitative Microbial Risk Assessment (QMRA) methodology.
In addition, detailed information on the greywater use practices of over 1000 Melbourne households was gathered to produce a robust dataset on microbial quality for the three most commonly used greywater types: washing machine wash water, washing machine rinse water and bath/shower drain water.
This data provided the basis of health risk estimates for consumption of home-grown produce irrigated with untreated greywater. This enabled in depth modelling of the health risks of norovirus infection, a common cause of gastroenteritis, associated with use of untreated greywater on selected home grown produce.
The Outcome
Water restrictions were cited as the most common reason for using greywater, followed by pursuit of sustainable living principles. Reductions in greywater use over the study period were reported by more than half of greywater users. These changes were most commonly attributed to increased rainfall, relaxation of water restrictions and installation of a rainwater tanks. Greywater was most commonly collected from the laundry, followed by the bathroom and the kitchen, and is generally used without further treatment. The most common uses of greywater were watering gardens, pot plants and vegetables via surface irrigation,
More than one third of households had changed household products or reduced the amount of product used to improve the quality of greywater collected.
Nearly half of households were aware of EPA Victoria guidelines on greywater use, but this did not influence non-recommended practices such as using greywater to water vegetables that were to be eaten without cooking.
On the basis of 2011 estimates, greywater using households collected 14.9 litres per person per day, averaged over the whole year. This equates to collection and reuse of about 10 per cent of total water use for an average Melbourne household.
Levels of faecal contamination in greywater from the laundry and bathroom were highly variable, as measured by concentrations of the indicator bacteria Escherichia coli. However, quantitative microbial risk assessment modelling of the average disease burden across the whole Melbourne population indicated that health risks fell far below the target levels specified in the Australian Guidelines for Water Recycling under all the scenarios assessed.
