What we think we know about “healthy” choices and what’s actually true can fall out of sync. According to new research, that may be especially true when it comes to how safe we assume bottled drinking water really is.

In September 2025, a team led by researchers at Washington State University published their findings in theJournal of Water and Healthexamining the differences between people’s beliefs about how “clean and reliable” their drinking water is and the results of lab tests in those same households.

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The team focused on communities in the Western Highlands of Guatemala, where they surveyed 60 households, 30 in urban areas and 30 in rural communities. They also collected drinking water samples from bottled, piped, well, spring, and filtered sources in both regions and tested them for coliforms, Escherichia coli, and other bacteria.

In the survey, most respondents believed “large, refillable jugs” were the safest option for drinking water. However, when the water was tested, that source showed the highest coliform contamination. The Washington State Department of Health explained that coliforms are “organisms present in the environment and in the feces of all warm-blooded animals and humans.” Although the agency noted that coliform bacteria are unlikely to cause illness, their presence in drinking water “indicates that disease-causing organisms (pathogens) could be in the water system.”

“We found there is a clear disconnect between what people believe about water safety and what’s actually happening in their homes, and that can have major public health implications,” Dr. Brooke Ramay, lead author and assistant research professor in the WSU College of Veterinary Medicine’s Paul G. Allen School for Global Health, said in a statement. “When people believe their water is safe, they don’t take extra precautions, but when they see a risk, they change their behavior.”

The researchers noted that despite the belief that bottled water is safer, it was “six times” likely to test positive for coliforms than the other sources. Perhaps most alarmingly, only 17% of the bottled water they sampled met the World Health Organization standards for safe drinking water. That’s especially concerning in places like Guatemala, where access to clean public drinking water is difficult or impossible for manyforcing people to purchase bagged or bottled water often. As the researchers explained, many in Guatemala also refill the same water jugs at purification plants or neighborhood refill stations, where the water is treated and sealed.

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“The problem isn’t usually with how the water is bottled — it’s what happens afterward,” Ramay added. “These jugs can be stored improperly, and dispensers aren’t cleaned regularly, and we think this can create ideal conditions for bacteria to grow.”

While the bottled water did not perform well in these tests, neither did other sources. The team found coliform bacteria in 90% of samples, along with CRE, a “particularly concerning form of antimicrobial-resistant bacteria,” detected in some piped household water samples.

The study also highlighted a significant disconnect between public perception and factual information about municipal water safety. The team found that although survey respondents ranked it lower in perceived safety, the water tested from protected municipal wells had the lowest on-site contamination rates, with no samples testing positive for coliforms or for detectable E. coli, ESBL, or CRE bacteria. But the picture changed once the water moved through household plumbing. In samples taken from water piped into homes, than 65% tested positive for coliforms; about 28% had E. coli, and 11% tested positive for ESBL and CRE.

Although this study took place in Guatemala, it has global implications, including in your home, too. As the researchers concluded, our cultural beliefs about water can influence our behavior and health: if you never question where your water comes from, you’re less likely to treat it, or, in the case of bottled water, clean the dispensers often. Ramay added, “Our results suggest that beliefs about water safety may actually contribute to contamination because people don’t take the same hygienic steps with sources they trust that they might with other, less trusted sources.”

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