In a small brick shed in the Southern Highlands eight tiny fish stand guard, 24 hours a day, seven days a week, over the water flowing to more than 4 million people. Like the canaries that once sniffed the air in coal mines, the Australian rainbow fish are living proof that the city's water is safe. If they don't like what they are swimming in, they have the power to shut down much of Sydney's supply system. Although the Sydney Catchment Authority routinely tests for a wide range of impurities, the checks only guarantee water quality at the moment they are conducted. Khanittha Poonbua, a project engineer with the authority, said the the three centimetre fish provided continuous evidence that all is well.
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