70% of the bottled water sampled by researchers in Montreal showed high levels of heterotrophic bacteria. This calls into question the benefits of switching to bottled water in cities with clean tap water.

The researchers randomly purchased several brands of bottled water from a local marketplace and subjected them to microbiological analysis. They discovered more than 70 percent of famous brands tested did not meet the United States Pharmacopeia (USP) specifications of 500 cfu/mL, and in some cases the water was 100 times richer in bacteria than recommended.

The average microbial count for different tap water samples was 170 cfu/mL.

The bacteria are unlikely to cause disease although they could potentially affect people whose systems are already vulnerable.

“Bottled water is not expected to be free from microorganisms but the cfu observed in this study is surprisingly very high. Therefore, it is strongly recommended to establish a limit for the heterotrophic bacteria count as well as to identify the nature of microorganisms present in the bottled water,” says Azam.