Water

Boosting Water Supply the Smart Way
July 2009

By Matthew Giesemann
General Manager Engineering, City West Water, Melbourne, Australia

The earth lies some 150,000 kilometers from the sun, and this unique placement means that water can remain in a liquid state on our planet's surface. If the earth were any closer the sun, the water would be too hot or boil off into space. Any further away and the water would freeze.

Fresh clean water sustains all life on the planet, making water a precious and valuable resource. As the population of the earth grows and the earth becomes more polluted, clean water becomes scarcer. Everyone should make the best use of the remaining water we have. In this scenario, reusing water to help preserve the few remaining untapped reserves becomes an attractive alternative.

Many countries are now looking at how water can be reused. In fact, a number of water reuse schemes have already been initiated. The development of cheaper filtration and reliable disinfection technologies has made water reuse a feasible option in large cities.

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Recycled water can be used for washing down stock yards
SOURCE: City West Water

At City West Water (CWW), a retail water company supplying over 300,000 properties in Melbourne's Central Business District and inner and western suburbs, we have decided to ease our dependence on supplies of fresh potable water by supplementing the use of potable water with reused water. This makes perfect sense when:

• the demand for potable water continues to grow as populations grow
• in most cases, all the local supplies of fresh water have been exhausted and it is becoming more expensive to bring water to the city from greater distances
• harvesting water from new sources can have a significant detrimental effect on the environment from which the water is taken
• alternative sources of potable water such as desalination are expensive and definitely not greenhouse friendly
• reusing water reduces the need to dispose of wastewater to the environment.

Up to 80% of water entering a domestic property leaves it as contaminated wastewater. Reusing this wastewater can be just as cost effective as providing new supplies, particularly in circumstances where a wastewater treatment plant is just nearby and can easily respond to the demand.

Reused water is ideal for most industrial purposes. In domestic properties, reused water can replace water for flushing toilets, washing cars, washing outdoor surfaces, supplying ornamental water features, and even for fire fighting.

Wastewater from a domestic property can be categorized into ‘black water', which is wastewater from toilets and urinals, and ‘grey water', which is water from the rest of the house. It is possible to separate these within a domestic property with some minor modifications to internal plumbing. In such circumstances, the grey water can be treated and reused on site. The black water, however, contains harmful bacteria as well as billions of viruses and protozoa and must be sent to an appropriate treatment system for cleaning.

Alternatively all wastewater may be discharged to a centralized treatment plant where it is mechanically treated, producing an effluent and bio-solids. The effluent is a reliable source of reusable water and can be redistributed to nearby properties via a specially constructed distribution and reticulation network. Before distribution, additional treatment facilities such as filtration and sterilization may also be needed depending upon the use of the reused water.

At CWW, we have put in place training programs to ensure we have knowledge and skills to oversee the design and construction of these sorts of treatment facilities and, just as importantly, the competence to operate and maintain them. Adding reused water to your arsenal brings with it new risks. With suitable training and practice, these risks can be minimized, but should never be ignored.

Local School where the grounds are watered with treated wastewater.
SOURCE: City West Water

Effective regulation is required if wastewater is to be treated and reused. CWW works with its health and environmental regulators to ensure public health is maintained and there are no detrimental environmental effects as a result of its reused water schemes.

We protect public health by reducing the viruses and protozoa found in wastewater. The degree of reduction required depends on how the reclaimed water will be used. You'll need reductions in the order of ten million times where human contact is likely, such as the watering of domestic gardens. In addition, some assurances are required that these reductions will continue into the future through the use of good management practices.

The continued application of reused water to land can result in the build up of toxic substances. Environmental regulators limit this by placing upper limits on the concentration of pollutants remaining in reuse water after treatment. In some cases, users of recycled water are required to have management plans in place to ensure proper practices are maintained. CWW works with its customers to help them develop these plans.

The community can be reluctant to accept reused water and consultation and public information and education programs are needed to gain acceptance of this new product.

Reused water can provide a sensible substitute for potable water, effectively easing existing supply problems or deferring the need for new sources to be brought online. There is plenty of opportunity to reuse water without resorting to direct potable substitution. Of all the water supplied to a city, the actual amount consumed or used in cooking is only a few percent.

It will take some time to develop a water reuse scheme but the rewards can be great. Technologies exist to ensure reuse water is safe but the knowledge and skills in the use of these technologies need to be developed and retained, and this must be part of any reuse scheme. The engagement of the Government and the community in the development of a scheme will go a long way to mitigating adverse reaction, which is often the result of misinformation.

Reused water can be a cost effective solution to a water shortage. However, not all situations will be suitable and the early identification of viable opportunities will help in saving unnecessary investigations and the consequential frustrations. Remember, reusing our resources will help save our environment and preserve what resources are left for future generations to enjoy.

• Dousing Melbourne's Dry Spells with Recycled Water
• City West Water^*
• Melbourne Water^*