The truth about water bottle hygiene: Are you cleaning it enough?

Every sip from your reusable water bottle could expose you to millions of bacteria if it's not properly cleaned, posing potential health risks.

According to new research, scientists now advise strict hygiene measures to keep drinking vessels safe, Caliber.Az reports.

Carl Behnke, a food safety expert at Purdue University in Indiana, USA, was shocked when he tested the cleanliness of his own reusable water bottle. After swiping the inside with a paper towel, he noticed it turned from white to grimy. This inspired a study in which Behnke and his colleagues examined the hygiene of bottles used by passers-by at the university. Many participants declined to hear their results, already suspecting their cleaning habits were inadequate. Unsurprisingly, their water bottles were found to be teeming with bacteria.

Studies show that bacteria thrive inside reusable bottles, particularly when water is left at room temperature. Primrose Freestone, an associate professor in clinical microbiology at the University of Leicester, explains that bacteria multiply in environments around 37°C (98°F) but can still flourish at lower temperatures. Research from Singapore found that water bottles contained an average of 75,000 bacteria per millilitre in the morning, which skyrocketed to 1-2 million bacteria per millilitre within 24 hours.

Most bacterial contamination comes from the user. Saliva, hands, and external surfaces introduce microbes into the bottle, including E. coli, which is associated with poor toilet hygiene. Sharing bottles can also transmit viruses like norovirus. Additionally, using bottles for drinks other than water, such as protein shakes, coffee, or juice, fosters even more microbial growth, Freestone warns.

While not all bacteria are harmful, those with weakened immune systems may be more vulnerable. Certain bacteria, including antibiotic-resistant strains like Klebsiella grimontii, have been detected in some bottles. Though no direct illnesses have been conclusively linked to water bottle contamination, experts caution that hygiene is crucial to avoid unnecessary health risks.

Behnke’s research found that people who washed their bottles using dishwashers or brushes had lower bacterial counts. However, many failed to clean them effectively or frequently. Freestone recommends washing bottles thoroughly with hot water (above 60°C), using washing-up liquid, and letting them air-dry.

Simply rinsing with cold water is insufficient, as it fails to remove biofilms—slimy bacterial layers that cling to surfaces. Bottles should be cleaned after every use or, at minimum, several times a week. If an odour develops, Freestone advises discarding the bottle altogether.

The choice of bottle material also matters. While plastic bottles tend to harbour more bacteria than stainless steel ones, the ability to clean the bottle thoroughly is the most critical factor. Additionally, plastic bottles can leach chemicals into the water, prompting concerns over potential health effects. Glass or stainless steel alternatives may be safer choices.

Regardless of material, the key takeaway is simple: maintaining rigorous hygiene is essential to ensuring that the water you drink remains safe and free from harmful bacteria.

By Aghakazim Guliyev