.

Effluent … inside the Tank Stream, which provided the original water supply for the city. Photo: Janie Barrett

SYDNEYSIDERS would rather drink highly purified sewage as part of a planned recycling scheme than consume the smaller amount of effluent already present in the city's water supplies, researchers have found.

The study, carried out with US researchers, suggests that the ''yuck factor'' associated with recycled sewage can be overcome once people learn they already drink it.

The findings coincide with a state government review of Sydney's water plan, as reported in yesterday's Herald, which will examine the viability of adding treated effluent to drinking water five years after Labor rejected the idea.

About 60,000 residents in Richmond and Windsor drink a mix of recycled sewage, stormwater and river water. Treated effluent is discharged from sewage treatment plants along the Hawkesbury-Nepean River before being collected and re-treated at North Richmond and delivered to homes.

Warragamba Dam, which supplies 80 per cent of Sydney's water, also contains small concentrations of effluent released into rivers that feed the dam.

Recycled wastewater indirectly enters the drinking water systems of other cities around the world, including London.

Despite its ubiquity, community acceptance of drinking treated sewage remains the barrier to introducing planned schemes in Australia.

Research conducted in Sydney last August, alongside that in the US states of Nevada, Oregon and Virginia, found that teaching people about the urban water cycle, including the presence of treated effluent, increased their acceptance of planned schemes.

"As soon as we introduced the issue of the water cycle, and people understood that water went round and round, it certainly seemed to open a lot of minds," said Ian Law, a water consultant and the lead researcher of the Australian arm of the study.

Drinking highly purified effluent from a planned recycling scheme was also preferred to drinking existing supplies that also contain effluent, but are not treated to the same level, the research found.

The study was conducted by the WateReuse Research Foundation in the US. The findings will be presented in Australia next month.

The national water commissioner, Chris Davis, who will advise the Sydney water plan review, said the public had a "mental block" about the effluent they already consume.

"Because it went into a river, people conveniently forgot where it started and no one really seems to mind," he said.

Labor's environment spokesman, Luke Foley, said issues such as water-saving measures and industrial water recycling should be considered first.