💧 Contaminated water: when intuitions poison

A scientific study reveals a striking gap between the perception of water safety and actual contamination data. Residents place their trust in sources that, in reality, pose significant health risks, while others, less esteemed, turn out to be cleaner.

Researchers from Washington State University conducted a survey in the Western Highlands of Guatemala, comparing local beliefs about water quality with laboratory analyses. They found that bottled water, often perceived as the safest, showed the highest contamination rates among the eleven types tested.

This water, packaged in large reusable containers, was six times more likely to contain coliforms, bacteria indicating fecal pollution, than other sources. Only 17% of bottled water samples met World Health Organization standards for drinking water. In contrast, protected municipal wells, although less appreciated, showed the lowest contamination levels.


The study involved sixty households, divided between urban and rural areas, where water samples were taken from various sources such as bottled water, tap water, wells, springs, and filtered water. The analyses looked for coliform bacteria, Escherichia coli, as well as strains producing extended-spectrum beta-lactamases or resistant to carbapenems. The latter are particularly concerning because they resist many common antibiotics and can cause infections that are difficult to treat, even if they often remain harmless in the digestive system.

Contamination was not limited to bottled water. Overall, 90% of samples contained coliforms, 55% E. coli, and 30% ESBL bacteria. CRE, rarer, were detected in some tap water samples. This presence in drinking water is alarming because it promotes the spread of antibiotic resistance, a global public health issue. Over four billion people lack access to safely managed water, and fecal contamination contributes to millions of cases of diarrheal diseases each year, especially in young children.

Cultural beliefs play a key role in this phenomenon. People who trust their water source are less likely to boil it, treat it, or regularly clean dispensers, as is the case for water containers. This lack of hygienic precautions can create conditions conducive to bacterial proliferation. Thus, the perception of safety can unintentionally worsen risks by reducing protective behaviors.

These results, published in the Journal of Water and Health, raise questions about public health strategies. Ultimately, this research highlights the need to bridge the gap between perceptions and scientific reality. Targeted interventions, such as awareness campaigns and better water quality monitoring, could help protect communities from invisible but dangerous contaminations.

The bacteria indicating water contamination

Coliforms are a group of bacteria commonly used as indicators of water quality, as their presence often signals fecal contamination. These microorganisms are not always pathogenic themselves, but they indicate that the water has been in contact with fecal matter, which can introduce more dangerous pathogens like Escherichia coli. In the Guatemalan study, the detection of coliforms in 90% of samples shows widespread contamination, highlighting public health risks.

Escherichia coli, or E. coli, is a specific bacterium often associated with fecal contamination and capable of causing serious intestinal infections. Its presence in 55% of water samples in Guatemala reveals a high level of exposure to pathogens. Unlike general coliforms, E. coli is more directly linked to diseases like diarrhea, particularly in children, which is why it is closely monitored in international drinking water standards.

Bacteria producing extended-spectrum beta-lactamases and resistant to carbapenems represent a growing threat due to their antibiotic resistance. They can survive in water and spread even without causing immediate illness, contributing to the emergence of superbugs. Their detection in drinking water, as in 30% of samples for ESBL, underscores the importance of rigorous controls to prevent the spread of antimicrobial resistance in community environments.