Researchers at CSIRO have for several years been investigating the feasibility of diverting urban stormwater and treated effluent into underground aquifers, where it can be recycled for use on parks, gardens, ovals and farms. The idea is to harvest surplus water during the wet part of the year, store it underground for some months, then bring it to the surface again for irrigation during the dry season.

Researchers consider these underground dams a unique solution to the problems of water storage, water conservation and recycling. The water will be injected into appropriate aquifers, where it is protected from evaporation or pollution - and does not submerge valuable land or habitat, as does a surface dam.

Microbiologist Simon Toze has produced clear evidence that storing water underground also purges it of disease-causing organisms, making it clean enough to recycle as irrigation. "We've been studying the behavior and fate of various microbes in ground water taken from different parts of the country," he explains. "We've looked at enteric (gut) viruses, the protozoan cryptosporidium, and disease-causing bacteria like salmonella and aeromonas. If we are to store large volumes of water underground for recycling, we need to know exactly what happens with these bugs, and whether they can survive in reclaimed water."

Once underground, the disease-causing organisms face a hostile array of conditions such as temperature changes, lack of oxygen, lack of nutrients and a whole army of naturally occurring ground water microorganisms that kill or inactivate them.

In experiments undertaken in aquifers and under controlled conditions in the laboratory simulating conditions of an underground aquifer, results have shown that the disease-causing microbes can last less than one month, Toze has found. "This makes underground storage one of the most promising ways to cleanse and recycle water," he says. "Australia is naturally a dry continent, and in many areas our ground water resources are being heavily exploited. This appears to offer a safe, clean way to recharge them. We also need to think about our environment, and the importance to natural streams and wetlands of maintaining adequate subsurface water supplies."

Toze has tested the antiviral activity of indigenous microbes in ground water.

In every case the large numbers of virus added to the water disappeared in less than six weeks. "Since water injected into an aquifer is likely to remain underground for several months before being re-used for irrigation, it looks as if there will be a comfortable safety margin," he notes.

"At present people still describe this as 'wastewater' - but that is a bad term, and it shows how limited our thinking still is towards water. Instead, people need to focus on the productive uses of reclaimed water. This sort of water is not intended for drinking, but for the irrigation of parks, gardens, farms, ovals and street verges," says Toze. "I believe that in pioneering this sort of water re-use, Australia is showing the world a lead in a field that will be increasingly vital to the human and environmental future."

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