Drinking water, a source of life... and microorganisms

Contrary to popular belief, drinking water isn’t sterile: it contains 10-100 million microorganisms (sidenote: Microorganisms Living organisms that are too small to be seen with the naked eye. They include bacteria, viruses, fungi, archaea and protozoa, and are commonly referred to as “microbes”. What is microbiology? Microbiology Society. ) per liter! But not to worry, as previously shown by an Anglo-American study, these bacteria seem to feed our gut microbiota. Now Italian scientists have taken water samples from public fountains and domestic taps in the city of Parma with the aim of exploring microbial biodiversity in their city’s water and its effects on the gut microbiota of residents.

Water, a vehicle for significant bacterial diversity

Examining the samples, the researchers found that five bacterial species had a greater relative abundance, although with significant variability from one sample to another. For example, in one fountain, Acidovorax delafieldii represented more than half of the bacteria present, while in another the dominant bacterium was Sphingomonas ursincola, which made up a quarter of the bacteria found. Moreover, this variability was just as great in tap water. The five dominant species were no surprise, since they are known to be frequently found in drinking water. More surprising was the fact that a large proportion of the bacteria present in drinking water, whether from fountains or the tap, were unknown, a sort of microbial “dark matter” that scientists must now explore.

From a glass of water to the gut microbiota

Given that we drink about two liters of water per day, do these bacteria have an impact on our gut microbiota? Yes, say the researchers, who detected the bacteria in the stool of regular tap water drinkers, with presence profiles that reflect the composition of the water consumed. In other words, day in, day out, tap water helps shape our gut microbiota. The researchers even showed that some bacteria appear to settle permanently (and remain even when we drink bottled water), while the presence of others seems closely linked to regular consumption (they disappear when we drink bottled water for several days).

These preliminary findings are somewhat incomplete but they open two fields of research still only superficially explored. Firstly, what bacteria are present in drinking water? Secondly, what influence does the water we drink have on our gut microbiota and our health? Water still has secrets hiding below the surface...