KEY POINTS:
The water crisis in Australia has given focus to the use of sewage as a source for reclaiming water to recycle as community supply.
Queensland premier Peter Beattie says that "because of the drought, all of Australia is going to end up drinking recycled purified water".
Inevitably there is a "yuk" factor associated with the idea of drinking water that has previously been in contact with human waste - particularly if it comes from someone else.
But there is ample precedent internationally of recycling reclaimed water for community use and for individual households.
Such measures have generally been driven by high community growth rates in water-short areas, or prolonged drought, or both - as in parts of Australia.
Another factor driving the interest in reclaimed water use is environmental. Stringent standards for discharging treated effluent into rivers and lakes increases the already high cost of treatment. So why "gold plate" effluent and then throw it away?
Reclaiming the nutrient value and water content of community wastewater, or sewage, has considerable precedent through the early "sewage farms" in Britain, where raw sewage was spread on land for agricultural benefit.
These days, treated effluents are being used to irrigate crops and recreational landscapes worldwide, including New Zealand.
The largest food-crop irrigation scheme in Australia is the Bolivar, Adelaide, where 1200 growers on 4000ha of prime land are spray-and-drip irrigating reclaimed water on vegetable and fruit crops for local consumption and export.
But reclaiming water from treated sewage effluent to recycle as drinking water is another matter. Is it necessary and is it viable culturally and from a public health perspective?
In 1968, Namibia's capital of Windhoek commissioned the first direct potable reuse system in the world with highly treated reclaimed water piped to mix with natural water in the main city reservoir.
The combined water source is then processed at the city water treatment plant before distribution.
Pipe-to-pipe direct reuse has been investigated in Denver, Colorado, with a 1984 demonstration project proving its viability.
But although community support was evaluated by surveys, no one really seemed happy to be the first consumer on the line downstream of the injection point into the water supply network.
Indirect reuse is common in many parts of the world, where wastewater effluent is discharged into rivers or groundwater aquifers which subsequently are used downstream as water sources.
In the United States, 525 cities have unplanned indirect reuse and about 15 million people use surface water supplies that contain at least 10 per cent wastewater effluent. And four million rely on supplies that - during low river flows - are 100 per cent wastewater effluent.
The largest such indirect reuse in New Zealand is the Waikato River intake for Auckland.
Planned indirect reuse schemes in the US are the Los Angeles County 1962 Whittier Narrows groundwater recharge scheme, which uses highly treated effluent subsequently withdrawn in conjunction with natural groundwater for treatment and community supply.
This scheme was supplemented in the 1980s with the Water Factory 21 project in neighbouring Orange County.
Evaluations of these groundwater recharge operations over more than two decades show no adverse effects on groundwater quality or on people's health. The science, technology and practice of water treatment that can deliver high-quality drinking water from even the most polluted waste streams is well established on large and small scales.
The PureCycle household recycle system was introduced to Colorado in the late 1970s to replace septic tank systems in mountain retreat areas where groundwater supplies were limited by geology, and where there was no soil to soak up effluent.
The sophisticated treatment and monitoring systems proved entirely reliable, but the company was no longer operating by 1984, probably attributable to lack of demand from homeowners sceptical about the idea of drinking water sourced from their own household waste.
Fortunately, in New Zealand we do not have the combination of drought and water shortage that has prompted Australia to consider the direct reuse of water reclaimed from sewage effluent.
Even though the technology is available to secure high-quality water to the most stringent levels of health protection, we are likely to remain with the indirect approach for water supply supplementation, such as the Waikato-to-Auckland supply.
Non-potable use of reclaimed water is being used in some rural-residential subdivisions in Auckland and the Coromandel to flush toilets, but upgrading on-site wastewater systems - for example on Waiheke Island or around the Rotorua lakes - with PureCycle-type systems looks unlikely.
Meanwhile, as frequent visitors to Australia, many of us will have the opportunity to experience the benefits of Queensland's water supply mix of reclaimed and natural water sources.
* Ian Gunn is an honorary research fellow at the Department of Civil and Environmental Engineering, University of Auckland.
