Water Research Australia Water for the wellbeing of all Australians November 2013 Page 1

THE USE OF GREYWATERDrought conditi ons and subsequent restricti ons on outdoor household water use has led to increasing use of alternati ve water sources in Australia. Greywater is water that has been used once - in bathrooms (excluding toilet), laundries or kitchens, that is collected for reuse around the house or garden. It is a readily-available water source for households which can be collected and reused at litt le or no cost.

Greywater contains a range of chemicals from household cleaning products, laundry detergents and personal care products. It also contains variable levels of microorganisms, someti mes including pathogens (harmful microorganisms) that can cause gastroenteriti s. The risk of infecti on from such pathogens is considered to be the most signifi cant human health risk associated with greywater reuse.

This fact sheet summarises the fi ndings of a project that characterised greywater use practi ces and greywater quality in Melbourne households and assessed potenti al health risks from the use of greywater on home-grown produce.

STUDY DESIGNThe project had three components:• A survey to collect informati on from households on the

types of greywater collected and methods of treatment, storage and use. Households were asked whether they had used greywater in the current year or during any of the preceding four years. More detailed informati on was then collected from greywater users about the most recent year of use.

• Measurement of the microbial quality of the three types of greywater most commonly used by households (washing machine wash water, washing machine rinse water and bath/shower water).

• Combining the collected data with existi ng informati on to model potenti al risks of norovirus infecti on (a common cause of gastroenteriti s) that may be associated with the use of untreated greywater on home-grown lett uce.

GREYWATER SURVEY RESULTSThe survey was performed in suburban Melbourne in early 2011 using three methods to collect informati on (mail, telephone and internet). Over 1,600 households responded to the survey and more than two thirds of these had used greywater during at least one of the fi ve years in the study period.

• More than 70% of households using greywater collected the water from the laundry. Over 60% collected water from the bathroom, and about one third collected water from the kitchen.

• Most households used simple methods such as buckets or a hose from the washing machine to collect and distribute greywater. Greywater was mainly used without treatment and within 24 hours of collecti on.

• Greywater was most commonly used for surface watering of gardens (over 90% of users), followed by pot plants and vegetables/fruit/herbs.

• Nearly half of greywater-using households said they were aware of EPA Victoria guidelines about greywater use, but awareness did not reduce the likelihood of non-recommended uses such as watering vegetables/fruit/herbs to be eaten without cooking.

• More than half of greywater users reported changing their greywater use over ti me, mainly due to increased rainfall, relaxati on of water restricti ons or having a rainwater tank installed. Over 80% of those who had used greywater intended to keep using it in the future.

• Householders esti mated they collected about 15 litres of greywater per person per day, averaged over the whole year. This is equivalent to about 10% of average household tap water use in Melbourne in 2010/2011.

Greywater contains variable levels of microorganisms, someti mes including pathogens.

Fact Sheet Health risks of greywater use

Water Research Australia Water for the wellbeing of all Australians

GREYWATER QUALITYMore than 180 greywater samples from over 90 households were tested for E. coli indicator bacteria. These are harmless bacteria that are found in the digesti ve system of humans and warm-blooded animals. They are used to detect faecal contaminati on in water. Levels of faecal contaminati on in all types of greywater were variable. Bathroom water tended to have more E. coli indicator bacteria than washing machine water, but there was a lot of overlap in E. coli levels between the diff erent types of greywater.

More than 100 greywater samples were tested for pathogenic E. coli – these are types of E. coli which can cause gastroenteriti s and are diff erent from the harmless E. coli indicator bacteria that all people carry in their digesti ve system. Three samples were found to contain pathogenic E. coli. Tests for norovirus were performed on 40 greywater samples. Norovirus was detected in one sample.

The detecti on of these pathogens in some greywater samples was expected and should not be a cause for alarm. They were chosen for testi ng because they are the two most common causes of gastroenteriti s in Australia, and there was a good chance of detecti ng them even with a small number of greywater samples. Most cases of gastroenteriti s due to these pathogens are mild and only last 1 or 2 days.

HEALTH RISK ASSESSMENTA modelling approach was used to esti mate the possible risk of infecti on and illness from norovirus when using untreated greywater to water lett uce. This is a ‘high risk’ use because water can be trapped among the leaves, and lett uce is eaten without cooking (and someti mes without washing). Therefore, our modelling results represent a ‘worst case scenario’ esti mate.

Under the worst conditi ons (watering with poor quality greywater on the same day the lett uce is harvested and eaten, lett uce not washed before eati ng, dry year with high rate of greywater use), we predicted that fewer than 20 extra cases of norovirus illness associated with greywater use might occur in Melbourne over a period of one year.

This is a ti ny number compared to the large number of illnesses (about 400,000) due to this common pathogen that are esti mated to occur each year in Melbourne. It is also lower than the risk of illness from catching the infecti on from someone else in the same house.

OUTCOMES The health risk assessment indicated that, on a populati on basis, household greywater use presents a lesser health concern than many other exposure sources for gastrointesti nal pathogens.

The fi nding that knowledge of current guidelines did not infl uence non-recommended uses highlights the need for bett er promoti on and reinforcement of such guidance to the public.

This fact sheet is based on a report for Smart Water Fund Victoria Project 72M-7079 (WaterRA Project 3006-09) (November 2011) led by Associate Professor Karin Leder, Monash University.

This series of fact sheets was initi ated by the Cooperati ve Research Centre for Water Quality and Treatment (CRC WQT) in 2003. The fact sheets are largely based on research carried out in the CRC WQT and its successors, WQRA (2008-2013) and Water Research Australia (WaterRA, 2013 - ).

Since 2008 the research has been funded enti rely by the Members of WaterRA, who comprise Australian water uti liti es, universiti es, engineering and consulti ng companies and government agencies. Our Members provide annual contributi ons in the form of money, ti me, experti se and other in-kind contributi ons. The research conducted investi gates issues of concern to the water industry and will benefi t all Australians through improved water treatment and quality.

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Over 100 greywater samples were tested for pathogenic Escherichia coli (E. coli), which can cause gastroenteriti s ...

November 2013 Page 2