Every time you take a sip from your water bottle, you introduce bacteria into it, and over the course of a day, they can multiply up to several million times. Here's what scientists advise you to do to prevent this.
Karl Behnke has always wondered how clean his water bottle really is.
When he put paper towels in it and rubbed them on the walls of the bottle, a surprise ensued.
"The napkins were white until I took them out," says Benke, a food safety expert at Purdue University in Indiana, United States.
"That's when I realized that the feeling of the wipes slipping as I cleaned the inside of the bottle wasn't because of its material, but because of the bacteria that had accumulated," he adds.
Then he devised how to conduct the research.
Benke and his colleagues they stopped passersby in the hallways of the university and asked them if they would be willing to donate their water bottles for research purposes to determine how clean they were.
"What was particularly striking was the number of people who didn't want to know the results."
"Basically, they knew that the hygiene of their bottles was poor or that they weren't cleaning them at all, and the data later confirmed that," Benke recalls.
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The results showed that these bottles were full. bacterium.
The value of the global market for reusable water bottles in 2024 was around $ 10 billion.
A survey conducted among healthcare workers in Italy showed that half of them used reusable water bottles, and the proportion of users of these drinking bottles among students was between 50 and 81 percent.
Although they help us stay hydrated, carrying these bottles everywhere we go and regularly drinking fluids from them can pose a health risk.
So, should we not use them at all or is it possible to keep these risks under control?
What's actually inside water bottles?
Although tap water is generally safe to drink, it contains a certain amount of microorganisms.
So if you leave water in a bottle for a few days, it can encourage bacterial growth, says Primrose Freestone, associate professor of clinical microbiology at the University of Leicester in the United Kingdom (UK).
Bacteria that can cause infections in humans thrive best at temperatures around 37 degrees Celsius, but can also multiply at room temperature of around 20°C, Freestone explains.
"The longer the water stays in the bottle at room temperature, the more bacteria grows," she says.
Research conducted in Singapore, South Korea, using boiled tap water, which is supposed to eliminate most bacteria, showed that bacteria numbers can grow rapidly in bottles during daily use.
Researchers found that the amount of bacteria in water from bottles used by adults increased on average from about 75.000 bacteria per milliliter in mid-morning to more than one to two million per milliliter over 24 hours.
Fristone says one way to slow down the growth of bacteria is to keep the bottle in the refrigerator between uses, although this may not completely stop the growth of bacteria.
However, although some of the bacteria comes from the water itself, most of it actually comes from the user of the bottle.
Whether you take your bottle to work, the gym, or just keep it at home, its exterior will be teeming with microorganisms.
With each sip, those microbes are easily transferred to the inside of the bottle, along with bacteria from your mouth, Freestone explains.
Bottle users who don't wash their hands regularly can also introduce bacteria like E. coli into their bottles, she warns.
"If we don't take enough care of hygiene after using the toilet, bacteria associated with feces, such as E. coli, can end up on our lips from our hands," she says.
Also, sharing the bottle with others can spread viruses.
Diseases like norovirus can easily be transmitted this way.
People generally have between 500 and 600 different species of bacteria in their mouths, Freestone says.
"What won't cause infection for you doesn't mean it won't for others."
"You can be a carrier of the infection without even realizing it, because our immune system successfully protects our body," she adds.
Another way to encourage bacterial growth in a bottle is to pour anything other than fresh water into it.
The drinks that feed us also feed microbes, so drinks that contain sugar, for example, can encourage the growth of bacteria or mold in the bottle, explains Freestone.
"Anything but water is a haven for bacteria and fungi, especially protein shakes," she says.
If you've ever left milk in a glass for a few hours, you've probably noticed a thin layer that remains on the glass when you spill the milk.
Bacteria simply love that layer, says Freestone.
How can these bacteria affect us?
We are surrounded by bacteria in the soil, air, and on our own bodies, but it is important to note that most bacteria are harmless or even beneficial.
Water contaminated with bacteria such as Escherichia coli can cause diarrhea and vomiting, but not always.
Escherichia coli represents a large group of bacteria that are naturally found in the environment, but are also natural inhabitants of the human intestines.
Only when these bacteria become pathogenic, that is, when they acquire properties that make them harmful, can they cause disease.
Most microorganisms are not dangerous to humans, but those with weakened immune systems may be more susceptible to infections, Freestone warns.
Also, viral gastroenteritis or a stomach virus can sometimes cause long-term changes in the intestines.
“Our gut is constantly changing, but there are over 1.000 different species of microorganisms living in it, so it’s difficult to induce a change in composition,” says Freestone.
"There are too many variables to give a definitive answer, but poisoning yourself with bacteria from a water bottle certainly doesn't bring any positive changes."
People who have recently taken antibiotics, which can affect their gut flora, may become more susceptible to other infections.
A swab taken from a reusable water bottle in a newsroom in England revealed that these bottles can be a breeding ground for new strains of bacteria that are resistant to antibiotics.
In a sample from a water bottle, researchers discovered a type of bacteria Klebsiella grimontii which is capable of forming biofilm even on otherwise sterile surfaces.
Although this bacterium can be found in the normal microflora of the intestines, it can cause serious diarrhea in people who have recently taken antibiotics.
If mold or fungus develops in the bottle, it can cause symptoms in all who suffer from allergies.
However, it is important to note that there are no recorded cases of serious illnesses directly related to the use of reusable bottles in the professional literature.
Of course, this does not mean that such cases do not occur, because otherwise it is very difficult to accurately determine the exact source of infection.
How should reusable bottles be cleaned?
Karl Benke felt he needed to give his water bottle a thorough cleaning, and that was the trigger for him to take a closer look at what he found inside.
He used a bottle with a filter, but he began to notice that the water from it had an unpleasant taste.
"I would rinse it with hot water every now and then, and that would be it," he says.
After the paper towels revealed how dirty the inside of the bottle actually was, Benke and colleagues conducted a detailed study of people's habits regarding the use and cleaning of water bottles.
They found that just over half of the 90 respondents shared their bottles with others, while 15 percent admitted to never washing them.
The results were expected, as the level of contamination was directly related to whether someone rinsed or washed the water bottle at all.
However, Benke also found that the frequency of washing or the method of washing did not always have a decisive impact on the level of contamination inside the vials.
The insides of bottles that were washed with a brush or put in the dishwasher had the lowest concentrations of bacteria.
Benke and his colleagues point out that the most effective way to clean bottles is to wash them in a dishwasher with a disinfection program.
However, the study's conclusion emphasizes that the results may not be completely accurate, as the researchers had to rely on statements from respondents who may have given "more socially desirable" answers.
It was also discovered that bottles that held tea, coffee or juice were significantly more polluted than those that held only water.
Regular and thorough cleaning of bottles is the only way to ensure that you are not introducing harmful bacteria into your water.
Even if the water in the bottle is sterile, your saliva will inevitably end up inside, along with trace amounts of nutrients that are ideal food for bacteria, warns Freestone.
Rinsing the bottle with cold water is not enough, because it does not remove biofilms, slippery layers of bacteria that can form on the inner surface of the bottle, creating ideal conditions for their growth, warns Freestone.
She recommends washing these bottles with hot water (above 60°C), as this temperature destroys most pathogens, and that dishwashing detergent be used.
Pour water and detergent into the bottle, shake and let the liquid sit for 10 minutes, then rinse thoroughly with hot water.
The bottle should then be left to air dry, as microorganisms prefer a moist environment.
Freestone advises cleaning the bottle after each use, or at least a few times a week, and never waiting for it to start smelling unpleasant.
"If your cat starts to stink, you're already too late."
"Then it's best to throw it away," she says.
Once you've thoroughly cleaned the bottle, be sure to wash your hands before touching it, Freestone adds.
Benke now has completely different habits when it comes to using a water bottle.
She washes and air-drys it every week, uses bleach and a bottle brush to thoroughly clean the lid and all other parts.
Is there a type of bottle that should be avoided?
Although some research shows that plastic bottles have more bacteria than stainless steel ones, the cleaning method is much more important.
"The most hygienic bottles are the ones that are easiest to clean," says Freestone.
He adds that it is important to thoroughly clean all parts of the bottle, including the exterior, lid, and straw if there is one.
However, there is another reason why you should choose a metal bottle over a plastic one.
“Plastics typically contain chemical additives that give them useful properties such as flexibility, durability, heat resistance, and light weight,” says Amit Abraham, associate professor of clinical health sciences at Qatar.
"These additives are physically bound to the plastic, which means they can leach into the water," he explains.
Some research suggests that these supplements, poput bisphenol A (BPA), they can violate hormonal balance, and are also associated with an increased risk of heart disease, stroke, diabetes, and other chronic diseases.
These additives can leach into the water, regardless of whether the plastic bottle is single-use or reusable, says Abraham.
Also, i the same plastic It can begin to break down over time, increasing the concentration of microplastics in the water.
That's why glass or stainless steel bottles are safer.
However, whatever bottle you choose, the most important thing is to clean it thoroughly and regularly, as this will ensure that the water you drink is not full of harmful bacteria.
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