Using Greywater - An Update (February 2007)

The use of greywater in gardens has grown exponentially in the last year as the drought and water restrictions force gardeners to take a more active approach to keeping their gardens alive. Unfortunately, incorrect information on how to use greywater in the garden has appeared in newspapers and on radio gardening programs, and ill-informed home gardeners are making some terrible mistakes.

SGA has prepared two information pages on greywater, Greywater & Greywater Tanks, and Greywater Detergents. Both of these are essential reading for anyone contemplating using greywater in the garden. The Environmental Protection Authority (EPA) in Victoria also provides information on greywater use - outlining the dos and don't. Visit the website: http://www.epa.vic.gov.au/water/Reuse/reuse.asp. Check with the EPA or relevant water authority in your state.

Greywater Mistakes

Horticulturist Ken Fraser contacted SGA when clients informed him they had 'shandied' their greywater with their rainwater in a large concrete underground tank, in the hope that diluting the greywater would make it 'safer'. SGA advised Ken to have the water tested to ascertain the level of contamination.

The water test returned the result that E. coli was present but fortunately the levels were quite low. Escherichia coli is the gut bacteria found in human faeces that can be a dangerous contaminant if found at high enough levels in water. It is used as the 'indicator' of the pollution level of water. The tank was immediately emptied but specialised cleaning was not necessary because the E. coli levels were so low (this would have been an expensive exercise too).

E. coli doesn't usually live long or reproduce in ordinary water, as it's not the ideal environment for the bacteria. However, in greywater, the nutrient-rich environment can cause any E. coli present to grow exponentially, which is why we are instructed not to store greywater for more than 24 hours.

Horticulturist Kevin Walsh, author of Waterwise Gardening, mentioned to SGA that while giving talks in the drought ravaged Western District of Victoria he was shocked to discover that plants were dying of over-water and not from drought stress.

Apparently some home gardeners are not monitoring how much greywater they are diverting to their garden and are actually flooding their plants. In a household with many adults, the greywater output can be quite considerable and this should be taken into account.

Home gardeners are also failing to move hoses, so that only one area of their garden is receiving a huge volume of greywater. This is likely to not only cause over-watering and the subsequent death of plants, but can cause problems for neighbours who might be receiving all the run-off. Pooled greywater can also be harmful to children if they play in it and pets if they drink the greywater. It is illegal to allow your greywater to run off your property.

There has been little research conducted into the long-term effects of greywater on plants or soils, but SGA has discovered two people who are doing further research in this area.

WA Research

Well-known Western Australian horticulturist and SGA WA Patron, Josh Byrne is undertaking a PhD, investigating the role of wastewater re-use in sustainable urban landscapes.

He will be delivering the first of his technical papers at the Rainwater and Urban Design Conference in Sydney, 21-23 August 2007. For further information visit the website www.rainwater2007.com.

Josh's research is examining the water conservation benefits that can be achieved with effective wastewater reuse as part of an integrated urban water management approach. He is particularly interested in how the use of wastewater can safely be used to grow food at both the individual lot and public open space level in the face of a drying climate. His research ties in with the WA Premiers Water Foundation decentralised wastewater research program at Murdoch University, which is working with developers to demonstrate village scale decentralised wastewater recycling opportunities, which is discussed in more detail below.

Josh notes that village scale wastewater recycling initiatives not only provide a valuable source of water for our parks and gardens, but developers can actually save themselves a considerable amount of money as the result of reduced headworks in the construction phase. There are also opportunities for cost recovery via metering the wastewater and charging residents for usage.

Josh's research also includes a number of lot scale case studies across Perth where the irrigation performance of various greywater systems is being assessed. This includes the two gardens that he has recently set up on ABC TV's Gardening Australia program.

Victorian Research

Melbourne horticulturist Grant Harper's Masters research, being conducted at the University of Melbourne's Burnley College with funding obtained from the U.S. turf industry, is examining the effects of high levels of sodium and nitrates on Australian native grasses suitable for growing as turf grass (lawn). Sodium (as common salt) and nitrates are often high in grey water. Initially Grant was examining using wetlands to 'clean' greywater before reuse, but of course, establishing wetlands in the home garden is impractical, if not impossible in most situations.

His study involves examining a number of Australian native grasses suitable for turf, including Microleana stipoides, Danthonia richardsonii, and Chloris ventricosa (amongst others).

His study is some way off completion but Grant does point out a number of important factors to consider with greywater.

For example, Australian plants are not tolerant of high levels of phosphorous (P). Greywater can be very high in P, so finding detergents that have low levels of P is important (the website www.lanfaxlabs.com.au provides information on suitable detergents).

High pH (high alkalinity) will make P more available to plants. For this reason Grant suggests that monitoring the pH of the greywater is a very important factor.

High salt levels are also a problem, not just directly, but indirectly as high salt levels speed up the loss/breakdown of organic matter. Once again, the Lanfaxlabs website also has information on salt levels in detergents.

Soil Health is a Key

Maintaining soil health by adding plenty of organic matter is essential (even more than usual) to counteract the effects of any additional salt. It will also help to buffer the pH because another benefit of adding lots of organic matter is that it can help lower pH, which in turns makes less phosphorous available to plants (this is very important for native plants).

Grant also believes that irrigating turf with greywater is one of the best uses for this resource.

'I think using greywater on lawn is the way to go because lawns are so much a part of our thing - our culture,' he explains. 'But it's also the biomass that it generates. We can remove the excess growth by mowing and then composting it. The beauty of Australian grasses is that they require little irrigation, so if the greywater is not good quality it's not so important.'

Grant's website: www.harperconsults.com

New Subdivision Developments in WA

By June 2009, the WA State government will have completed a trial, in collaboration with local developers, including National Lifestyle Villages Pty Ltd, Peel Waters Pty Ltd, and Mallee Nominees Pty Ltd, to demonstrate and evaluate the performance, reliability, attributes and feasibility of decentralised wastewater recycling. The following is taken directly from the website: www.etc.murdoch.edu.au/pages/PWF_IS_01.pdf

Year 1 (2006) - Household-scale greywater recycling

During the first year the project will install a "Greyflow" greywater reuse system on each of 380 homes in the Bridgewater Lifestyle Village (National Lifestyle Villages Pty Ltd) in Erskine, Mandurah. Some houses will also be fitted with a constructed wetland to control nutrients. Researchers are now monitoring these systems at the site.

Year 2 (2007) - Village-scale greywater recycling

At the Timbers Edge Village (Peel Waters Pty Ltd) in Dawesville, Mandurah 260 houses will discharge their greywater into a large constructed wetland that in turn will provide treated water for irrigation of public open space around the village. As well as the technical aspects of re-using greywater the project will also address developer concerns over strata management and sub-contractor maintenance of such systems. Monitoring has also commenced at this site.

Year 3 (2008) - Village-scale wastewater recycling

Although the site is yet to be determined this part of the project is the most ambitious. All wastewater from 50-500 homes will be passed to a village scale wastewater treatment plant and then the treated wastewater will be used throughout the village for POS irrigation. Again issues of management, operation and maintenance as well as community education will be considered.

Conclusion

Greywater application to soil and plants is a new area of gardening, and scientific research appears to be thin on the ground. If you are aware of any additional research please contact SGA and we will follow up and continue reporting the latest cutting edge information to SGA gardeners.

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