By M. Titus, P. Krasonostein and J.C. Huggart

The purpose of this article is to support the argument that grey water, treated and recycled without harmful chemicals, is a sustainable water solution.

1. Grey water is produced everyday
“I have 11,000 litres of rainwater storage used to flush toilets.  No rain, no rainwater in storage.  I am interested in a grey water solution”

This is a quote from a prospective customer that arrived in an email on December 1st, 2006. The point is potent. Harvesting rainwater has made a substantial contribution to management of our precious and scarce water resources in Australia. If there is no rain, however, there is no rainwater available for toilet flushing or irrigation or anything else. In fact, rainwater collection systems often rely on mains backup and therefore, often potable water demand is not reduced at all.

The key benefit with grey water treatment is that the source is available every day.

Grey water is defined as the waste water produced from hand basins, bath tubs/showers and clothes washers. The waste water generated by toilets, kitchen sinks and dishwashers is not classified as grey water: it is blackwater1. The definition clearly identifies the sources of grey water and these are commonly found in all households, proving that grey water is produced every day in Australia.

The potential for recycled grey water use in Australia is extensive: water from the bathroom (baths, showers and wash basins) provides over 25 to 30 percent2,3 of the water that could be captured for recycling. This water contains pathogens from humans and chemicals and solids from soaps and shampoos. Over 95 percent of Australian houses have a washing machine4 implying that grey water from laundry is generated all over the country. Laundry water may contain elements such as phosphorus.

Treated grey water can be used for laundry. There is no difference, from a hygienic-microbiological point of view, between clothes washed with treated grey water or with drinking water. This has been established in overseas trials.5

Treating grey water further increases its reusability and reduces the amount of drinking water needed by each household. Homes and families can enjoy their water resources without restriction.

2. Demand on precious drinking water is reduced by 40 percent
Many regions in Australia are subject to increasingly harsh water restrictions. Recycling treated grey water for re-use for irrigation and within the home can reduce the drinking water requirement of each household by nearly 40 percent.

The benchmark water requirement is 247 L/person/day.6 Table 1 shows the water usage in 22 of the largest cities in Australia.7

Figure 1 shows the daily drinking water supplied to the gardens and waste water pumped to sewer after use in a typical four-person household (based on rounded average consumption values). If grey water is not recycled, all of the drinking water supplied to the house (excluding garden use) is pumped to sewers.

Figure 2 shows the amount of treated grey water reused in the house and gardens, reducing the water to sewer by around 60 percent and the drinking water supplied to the house by nearly 40 percent (based on rounded average consumption values).

One grey water system on the market today is able to produce 385 L/day for a typical four-person household. As 385 L is being supplied as treated grey water, demand for drinking water is reduced to 615 L. This is clearly displayed in Figure 2. Treatment and recycling of grey water saves 39 to 40 percent of drinking water.

3. Reduced chlorine discharge to the environment
Mains-supplied drinking water in Australia is typically treated with chlorine, which is an ozone-depleting gas.8 It is important to limit its release into the environment. Town drinking water contains five mg/L of chlorine induced at water treatment. Most grey water treatment systems also use chlorine for disinfection. Yet new grey water systems use UV disinfection instead, limiting chlorine’s effects on ozone depletion.

Recycled grey water comprises over 39 percent of the water being supplied to the household. This means that there is 39 percent less chlorine in the water supply and hence, discharged to the environment. If the 20.2 million9 population of Australia treated their grey water, there would be an annual chlorine reduction of 3,500 tons.

4. Treated grey water is good for your garden; your garden is good for the environment
The use of treated grey water can help to develop a greener Australia, which is both advantageous and essential. Aside from being a reliable source of water, it provides essential nutrients such as phosphorus, making it valuable for maintaining gardens.
The advantages of having more trees and plants are significant:

  • In a country where skin cancer poses a large threat, trees provide shade and protection from the sun.
  • Evapotranspiration (evaporation from the leaves) helps in cooling as it absorbs heat from the air.10
  • In the winter, trees serve as protection from the wind.
  • Trees increase evaporation. As more moisture from water bodies is evaporated and condensed as cloud; there is a greater chance of precipitation.11
  • Trees filter smoke, dust and ash from the air, making it cleaner to breathe.
  • Plants absorb carbon dioxide from the air and convert it to essential oxygen through photosynthesis. By absorbing this carbon dioxide, they help mitigate global warming and the greenhouse effect.12
  • Leaves from the trees create soil organic matter.
  • Roots of trees increase permeability. This retains water from storms and prevents runoff, reduces soil erosion and increases ground water recharge. It can be seen that trees and gardens are indispensable in maintaining a healthy environment.
  • Plants increase the aesthetic value of the area. They attract birds and other wildlife, making urban areas more pleasant to live and work in.13 This increases the productivity and hence the economy.
  • Plants produce fruit and vegetables.

Previously, devices have been used to divert untreated grey water to the gardens that had detrimental effects on the soil quality. Today’s treated grey water systems can be beneficial for the garden in comparison to untreated grey water.

Treated grey water contains essential phosphorus
A high concentration of phosphorus in untreated grey water is undesirable because it encourages algae growth in rivers. Algae utilize the oxygen reserve in the water body, killing marine life. Algae also blocks sunlight hindering any further plant growth. In addition to its impact on the environment, phosphorus is detrimental to humans. It is found in nature as phosphates, ingestion of which may lead to kidney failure and osteoporosis.14 Untreated grey water has a high phosphorus content of 10 to 15 mg/L and can be detrimental both to the environment and human health.

Treating the grey water reduces the phosphorus content to three mg/L, decreasing its threat to the environment. In controlled amounts, phosphorus can be highly beneficial to a garden because it is an essential element which acts as a natural fertilizer, reducing the need to add other fertilizers.15

Treated grey water has reduced thermotolerant coliforms
Untreated grey water has 1,000,000 to 100,000,000 cfu/100 mL of thermotol-erant coliforms. These pathogens can infect humans who are in close contact with untreated grey water, making it unsuitable for use in gardens growing fruit or vegetables.
Treated water from today’s grey water systems contains less than 10 cfu/100 mL, making it satisfactory for human contact. Furthermore, the UV disinfection used prevents regrowth of pathogens.16 Treated grey water is suitable for use in fruit and vegetable gardens.

Treated grey water maintains soil fertility and organic matter content
Soils are maintained at neutral conditions (pH 6.0 to 8.0) to preserve their fertility. The use of treated grey water does not affect the fertility because it is output at pH 7.0. The BOD (biochemical oxygen demand) content is less than 10 mg/L, preventing the risk of foul smelling odors in the garden because of organic matter decay.

Treated grey water will not pose water logging problems
Previously, common problems with diverted grey water usage were water logging and flooding. New grey water treatment systems can distribute water when required by the soil and pump the excess to sewers to avoid flooding.17

Treated grey water should not affect soil salinity
When recycling grey water with today’s new systems, it is important to use detergents that have potassium salts or liquid concentrates. The sodium salt concentration in the treated grey water will then be greatly reduced. Hence the use of treated grey water would not significantly affect the salinity of the soil.

Many salts are added to domestic grey water and these are primarily of sodium. The commonly found salts are sodium chlorides from the human diet, sodium nitrates from meat preservatives and food preparation, sodium sulphates, sodium tripolyphosphates and sodium carbonates from laundry products and sodium stearates from soaps. Due to the presence of these salts, using recycled grey water may increase the salinity of the soil.

Sodium salts are extremely soluble and cannot be removed from solution by precipitation nor can they be biologically degraded to non-ionic forms. Therefore, preventing these salts from entering the waste water stream is the most efficient method of reducing the high salinity hazard from recycling grey water. Laundry detergents and soaps are the primary source of the high salt concentration in grey water.18 In order to reduce the risk of high soil salinity, detergents using sodium salts are replaced by those using potassium salts or liquid concentrates.19

5. The systems are available today
Traditional solutions to address the scarcity of water will take time. You can take control today and install a grey water treatment system that saves water, money and the environment.

Most water used in houses in Australia is stored in dams or obtained as rainwater. A dam or a desalination plant takes a long time to build; a grey water treatment system can be installed in one day. The treated grey water is suitable for most household uses except as drinking water.

The Warragamba Dam of the Wollondilly region that stores 80 percent of Sydney’s water took 12 years to build.20 The dam announced to commence in 2008 on the Central Coast is projected to take up to 10 years to build and fill with the first water set available in 2013.21 Waiting for a drought to break is unpredictable and uncontrollable. It is essential to employ a system of constant water supply during such a time of decreasing annual rainfall.

6. Infrastructure and energy costs are reduced
The more houses that use grey water treatment systems, the less demand there will be on aging and constrained infrastructure and the less financial and environmental cost to manage distribution and waste treatment.
For a population of 20.2 million in Australia, nearly six billion kWh of energy is being used for sewage treatment and about five billion tons of greenhouse gas is released.22

Water requirement
If all of the houses for the current population are retrofitted with grey water treatment systems, 700,000 mL/annum of drinking water can be saved and would not need to be pumped to sewer (because the system treats and recycles 40 percent of the drinking water supplied).

104,000 new houses are built in Australia every year23. The average number of people in an Australian household is 2.624. If these new houses used grey water treatment systems, they would recycle 9,700 mL/annum of treated grey water.
The total treated grey water from all of these houses that would not be pumped to sewer is 710,000 mL/annum.

Energy requirement
The energy needed for sewage treatment in Sydney is 475 kWh/mL.25 Using this as a basis for all of Australia, employment of grey water treatment could save about 337 million kWh of electrical energy every year by reducing the power required to clean sewage. Greenhouse gas emissions can be reduced by 270 kilo tons.26

The cost of recycling non-potable water is estimated at $6/kL.27 12.8 gigaL of waste water is recycled annually in Sydney28 resulting in an operating cost of $77 million. The cost of operating a grey water treatment system is $6.30/kL which is around the same as the cost of recycling non-potable water. This implies that there is not a significantly increased cost for the users. Furthermore, if all of the houses employ grey water treatment, there will be a 60 percent reduction in waste water being managed at the municipal level potentially reducing non-potable water recycling operating costs.

Capital expenditure for water and waste water in Sydney for 2005 was $510 million.29 With a 60 percent reduction in the waste water being pumped to sewer, the equipment needed for sewage treatment is reduced and the capital expenditure may be reduced.

In 2005, Sydney Water spent $43 million to extend sewage services.30 With a reduction in the sewage being produced with grey water treatment, these expenses may be offset.

7. If every new or renovated house in Australia recycled their grey water, savings each year would be adequate to meet the drinking water requirement of Geelong
We know that 104,000 new houses are built and 34,000 are renovated every year in Australia.31 If all the new or renovated houses have a grey water treatment system, Australia can save about 12,600 mL/annum of drinking water which would have otherwise been used for toilet flushing and gardening. This is enough water to meet the annual drinking water requirement of Geelong (population of 125,38032).

If all of the current households of the 20.2 million Australian population used a grey water treatment system, 700,000 mL/annum of treated grey water would be recycled. This is enough water to meet the combined drinking water requirements of Melbourne and Sydney, the most densely populated cosmopolitan cities of Australia.


  1. ABS Dwelling Commencements, 2006, Cat No: 8750.0
  2. Australian Bureau of Statistics, 2006, Accessed from on 27th November, 2006.
  3. Australian Government, Department of the Environment and Heritage Australian Greenhouse Office, 2005, “AGO Factors and Methods Workbook”.
  4. Basix, 2006, benchmarking BASIX.
  5. Benson, S., 2006, “$342m for dam in Hunter”, Daily Telegraph.
  6. Brennan, M. J., Patterson, R. A. ,2004, “Economic Analysis of greywater recycling”, In Proceedings of 1st International Conference on Onsite Wastewater Treatment and Recycling organized by Environmental Technology Centre, Murdoch University, Perth.
  7. Commonwealth of Australia, 2006 “City Population”, Accessed on 4th December, 2006 from
  8. Dam, M., 2006, Accessed on 28th November, 2006 from
  9. Department of Infrastructure, Planning and Natural Resources, 2004, “Greywater Reuse Systems”, Preparation of Guidelines and Approval/Certification of Process Documentation.
  10. Dr. Patterson, R. A., 2006, “Consideration of soil salinity when assessing land application of effluent or greywater”, Lanfax Laboratories, Armidale.
  11. Fahey, D.W., 2002, “Twenty Questions and Answers about the Ozone layer”.
  12. Greywater, 2006, Sustainable sources, Accessed from
  13. Hunter Water, 2006, “Drought Proofing the Hunter and Central Coast”, Fact Sheet.
  14. Lenntech Water Treatment & air purification Holding B.V., 2006, “Phosphoru –P”, accessed on 28th November, 2006, from
  15. Maxey, A., 2005, “Greywater Regulations”.
  16. Marsden Jacob Associates, 2006, “Securing Australia’s Urban Water Supplies: Opportunities and Impediments”, FINAL REPORT.
  17. Rathjen, D., Cullen, P., Ashbolt, N., Cunliffe, D., Langford, J., Listowski, A., McKay, J., Priestly, A., and Radcliffe, J, 2003, “Recycling water for our cities”, Report to Prime Minister’s Science, Engineering and Innovation Council.
  18. Renovations Monitor, 2006, “Renovation Work Increases in Early 2006)”, HIA Economics group, Accessed on 23rd November, 2006, from
  19. Reynolds, E. R. C., Thompson, F. B., 1988, “Forests, Climate and Hydrology”, The United Nations University.
  20. Melbourne Cricket Ground, 2003, “MCG Facts and Figures”, Stadium Info, Accessed on 30th November, 2006, from
  21. NewsWales, 2006, “Welsh nuclear waste would fill four olympic size swimming pools”, Access on 28th November, 2006, from &F=1&id=8879
  22. NSW Recycled Water Coordination Committee, 1993, NSW Guidelines for Urban and Residential Use of Reclaimed Water.
  23. Sydney Water, 2006, “Strategic Framework”, chapter 2, Replacement Flows Project.
  24. Sydney Water, 2005, “Environmental, Social and Economic Performance”, Sydney Water Annual Report 2005.
  25. The Wollondilly Region of NSW, 2005, “Natural Attractions–Warragamba Dam”, Accessed on 23rd November, 2006, from dam.html
  26. U.S Environmental Protection Agency, 2006, “Trees and Vegetation, Heat Island Effect, Accessed on 28th November, 2006 from
  27. Water Corporation, 2002, “Using greywater”.

About the corresponding author
John C. Huggart is President and CEO of Nubian Water Systems. Contact him at

About the company
NUBIAN WATER SYSTEMS, PTY. LTD. 3/83-85 Whiting Street, Artarmon NSW 2064, Australia. Telephone 02 9438 5522; Fax 02 9438 5566; Email or visit the company’s website: The Nubian OASIS Greywater Treatment System utilizes UV disinfection to treat household grey water.


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