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Canadian researchers tested nearly a dozen brands of bottled water and discovered that 70 per cent had high levels of heterotrophic bacteria.

Another strike against bottled water.

New findings show that several types of bottled water sold in Canada contain high levels of bacteria, raising questions about the cleanliness and quality of bottling plants.

The health concerns add to the backlash against plastic-bottled water that has led several cities and school boards to impose bans.

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Canadian researchers from C-crest Laboratories Inc., a pharmaceutical product-testing lab in Montreal, tested nearly a dozen brands of bottled water and discovered that 70 per cent had high levels of heterotrophic bacteria. The findings were presented Tuesday at a meeting of the American Society for Microbiology in San Diego.

"This amount of bacteria is alarming, as if we are ingesting a cup of culture," said Sonish Azam, a researcher involved in the study who works at C-crest.

Health Canada doesn't have established limits for heterotrophic bacteria in water. But the United States Pharmacopeia, which sets quality, purity and other standards for drugs, food ingredients and other consumer products, says heterotrophic bacteria levels in drinking water should not exceed 500 colony-forming units (CFU) per millilitre.

The new research found that heterotrophic-bacteria levels exceeded that standard in 70 per cent of bottled-water brands tested. The highest recorded level was 80,000 CFU per millilitre.

Although the findings raise concerns, they also highlight how little is known about the health effects of heterotrophic bacteria. "These bacteria are mysterious. We just don't know what they are. It needs to be investigated in detail," Ms. Azam said.

The term heterotrophic bacteria is broad and can apply to many types of bacteria that get energy from carbon sources. Some of it can be pathogenic, or those that cause infectious disease, such as some types of E. coli.

The researchers said they didn't find pathogenic bacteria in the bottled water they tested. But they said some types of heterotrophic bacteria could be harmful to the young, elderly or pregnant women.

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Olga Naidenko, a senior scientist at Environmental Working Group, a U.S.-based advocacy association, said the risks associated with heterotrophic bacteria don't appear grave. But their presence serves as important indicators of overall hygiene and quality. High levels of bacteria, such as those found in bottled-water testing, may signal bigger problems, she said.

"What it tells us is that the system is not very good, that there may be leaks, that there may be some old bacteria in the walls," she said. "That's something that we as public-health professionals need to worry about."

The Canadian Bottled Water Association said that there is no evidence the bacteria is a health concern and that they can be found naturally in fruits and vegetables. "You have bacteria everywhere and this is a common phenomenon," said Michel Lavallée, technical director of the association.

Health Canada says that bottled-water manufacturers must follow comprehensive rules and that it has a similar safety level as that for tap water.

But many advocacy groups question the safety of bottled water, saying plants are tested less frequently and are subject to less stringent oversight than government-run water facilities.

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