According to a new Drexel University analysis, an increase in cases of gastrointestinal illness in the US was linked to cloudy drinking water, even though the water was within allowed limits.

Anneclaire De Roos, PhD, associate professor in the Dornsife School of Public Health, reviewed past studies from cities across North America and Europe and found an association between the cloudiness or opacity of drinking water and acute gastrointestinal illness (AGI).

According to de Roos, “More than 10 studies found a link between water turbidity and AGI incidence. These results suggest that exposures through drinking water caused a low but detectable number of AGI cases in the regions and time periods studied. There is no clear, alternative explanation for the patterns of associations — particularly when a similar pattern was seen multiple times.”

Cases of acute gastrointestinal illness generally occur as a result of waterborne pathogens such as norovirus, Giardia, or Cryptosporidium, and carry symptoms like diarrhoea and vomiting.

Cloudiness in water is caused by material floating in it, which are thought to provide some protection for harmful pathogens against disinfectants. Cloudiness in water could also be a sign that there is runoff into water sources that could contain harmful pathogens as well as sediment.

De Roos and her team also looked at various studies carried out around whether turbidity could be a good indicator of issues with pathogens in drinking water supplies, and found that turbidity of drinking water was linked to increased acute gastrointestinal illness in multiple studies, and not just when there was increased cloudiness.

As expected, the association between turbidity and AGI was found in cities with relatively high turbidity levels, often in unfiltered drinking water supplies. The findings that go against the conventional wisdom are the associations between turbidity and AGI that were seen at very low levels of turbidity — levels lower than the regulatory limits,” said de Roos.

According to de Roos, it is vital that one understands the reasons for the differences in the levels of turbidity in the various studies, so future research should focus on the specific conditions under which turbidity leads to AGI.

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