Credit: John Bull/COSMOS
With technological advances in recent years, recycled water can be made to be purer than rainwater. However, treating water is an expensive process, so usually, recycled water is treated to the extent needed for its purpose. For example, water used to douse pastures for cows is not treated nearly so comprehensively as water piped to people's homes. At Bolivar in South Australia, the treated effluent is collected and then treated as if it were drinking water, passing though filters and disinfection before travelling on to the garden tap at Mawson Lakes. In theory it could be drunk, although SA Water does not recommend you do, just in case.
Membrane filtration is a method gaining popularity amongst the water engineers. Filters can now remove even salt from the water. Microfiltration, nanofiltration, ultrafiltration and reverse osmosis (R.O.) are able to strain out ever more tiny particles from the water. R.O., the most rigorous filter, capturing anything bigger than 0.001 micrometres - or a billionth of a metre. Bacteria, by contrast, are lumbering giants at 1 micrometre; viruses measure up at 0.01 micrometres. So there is no chance of these pathogens appearing in water filtered by reverse osmosis. And yet many of these can be found in rainwater.
The downside to this super purity is the amount of energy required to pump the water through the membranes. Desalinated seawater using reverse osmosis was once famously described by former New South Wales Premier Bob Carr as "bottled electricity". Polishing wastewater with reverse osmosis would take the same, or at least very similar, amount of grunt. Thankfully, except where the wastewater was very salty, R.O. would not be necessary, ultrafiltration would be sufficient to remove bacteria and viruses from the water. And if you didn't want even to use that, chlorine or ultraviolet light will dispatch the nasties so they don't harm anyone drinking them.
Nonetheless, the electricity used in wastewater treatment is its biggest drawback. Even if the water passes through sand filters by gravity, pumps are still needed to get the water to, from and around the treatment plant and pumps use power. A lot of power.
If recycling were to be more widely adopted, significantly more energy would be required to bring the water up to scratch. Particularly for places like Sydney where the sewage treatment at some of their major plants is nothing more than a perfunctory straining before it is pumped out to sea.
Most sewage treatment works around Australia treat the waste more thoroughly than Sydney, especially since state government environment protection agencies were formed in recent years. The majority of treatment plants already spend a lot of energy cleaning up wastewater - just so they can dump it into the ocean or rivers without causing undue harm to the aquatic life. Bringing the wastewater up to reuse standard is often just one step extra.
For people like Anne Howe at SA Water, the decision to reuse much of the Bolivar water for Mawson Lakes and local agriculture was a no-brainer. "The wastewater has got to be cleaned up so you can dispose of it safely and not do damage to the coastal environment," she said. "It's the fact that we are, for environmental reasons, investing huge amounts of money to clean up the water before it is discharged into the ocean, and that seems a waste."
Australia is a young country. For the 50,000 or so years before to Europeans arrived, there was more than enough water for the tiny population, which might have been as high as 1 million. Since that time, the population has soared to more than 20 million, to the point where the water supply in this dry continent is unequal to demand.
For decades, water has come from the sky, fallen into dams, travelled to people's houses, and then passed through the sewer to the ocean. As the population grew, the engineers built bigger dams. When the sewers were affecting water quality on the beaches, engineers devised better water treatment. And so it grew, patch upon patch, engineering solution built on top of existing engineering solution of an otherwise old-fashioned system.
But now it's clear the old ways of doing things won't work any more. Australia's population has ballooned 20-fold, and climate change is about to make things worse: where rain once was plentiful, it is likely to decrease. Cities used to high rainfall may no longer be able to depend on it.
Now is the time to walk away from the thinking of yesteryear and embrace the concepts that will assure the nation's water supply into the future. The linear flow of water from sky to houses to sewers is not a sustainable practice. Better to 'close the loop' - as they say in the environment industry - and reuse the billions of litres we throw away every day.
Although Australians live on the driest inhabited continent, there's enough rain falling to feed its burgeoning population. Sydney, a city of more than 4 million people, receives 1,217 mm of rain a year; Brisbane 1,146 mm. Even arid Perth gets 773 mm.
Drizzly old London, by contrast gets just 611 mm - and that is a city of 7.3 million. Yet London has not had water restrictions for 15 years. But then, London does drink recycled water.
Sara Phillips is a senior editor of COSMOS, and the founding editor of G: The Green Lifestyle Magazine. This story won her a 2006 Reuters-World Conservation Union Award for Excellence in Environmental Reporting.
