If you think cloudy drinking water is purely a harmless aesthetic issue, think again. A new study conducted by researchers from Drexel University has revealed that murky drinking water is associated with an increased risk of stomach upsets, sometimes even when it is within the safety limits for water turbidity set by city water safety officials.
Dr Anneclair De Roose, an associate professor at Drexel University's Dornsife School of Public Health, conducted a review of previous studies that looked at the health effects of water turbidity undertaken at several cities across Europe and North America. She found a link between water turbidity — cloudy water — and acute gastrointestinal illness (AGI) in more than ten studies.
Waterborne pathogens such as Cryptosporidium, Giardia and norovirus can cause gastrointestinal illness with symptoms that include vomiting and diarrhea. It is estimated that in the US alone, between 12 to 16.4 million people fall ill with AGI each year as a result of being supplied contaminated water.
Since water turbidity is caused by particles held in suspension, it is thought that these suspended particles may in fact provide a hiding place to protect disease causing pathogens against chemicals used in the disinfection process. Cloudy water can also be an indication that water is contaminated by sediment and other harmful pollutants that have washed into the water source with runoff.
In order to gain a clearer understanding of whether cloudy water could be used as a tool to indicate whether pathogens are present in drinking water, De Roos and her team assessed a number of previous studies that focused on this issue. The goal of these earlier studies was to assess the risk of contamination of drinking water sources (typically rivers that provided the study cities with water), before water was piped into the city's water distribution system. The earlier studies correlated the level of water turbidity with the number of residents falling ill as a result of acute gastrointestinal illness, on a daily basis.
After analyzing the previous studies, De Roos determined that turbid drinking water led to an increase in AGI in several of the studies, and not only when drinking water became increasingly cloudy.
"As expected, the association between turbidity and AGI was found in cities with relatively high turbidity levels, often in unfiltered drinking water supplies," De Roos said. "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."
One of the study cities, Philadelphia, showed a link between cloudy drinking water and AGI reported in children and older citizens. Yet water turbidity reported in the studies, which were conducted in the 1990s, was in fact relatively low by both current and past standards.
Because there was some variation in terms of the level of water turbidity that were associated with AGI in the studies, De Roos stresses that it is important that we understand the reason why this is so. Future research on this topic should aim to identify the specific conditions that results in turbidity causing AGI.
"For example, given a similar range of turbidity, is the association with AGI restricted to a certain season or certain climatic conditions, such as periods of heavy rainfall?" De Roos said. "Furthermore, does the association disappear if a different treatment method is used -- like UV disinfection versus chlorination alone?"
This could help identify specific conditions that lead to turbidity causing AGI, which would in turn assist water utility managers to monitor their water quality data to quickly spot conditions that may make the water supply vulnerable to contamination.
"While these types of epidemiologic studies can't give definitive answers, they offer a relatively inexpensive tool for screening water supplies in order to prioritize management strategies and further research," De Roos said.
