Reusable water bottles are becoming increasingly popular, largely due to their eco-friendliness and convenience. However, there seems to be a bit of confusion on social media about how to keep them clean. People often share unsettling images of mold developing inside their bottles.
According to Kelly Reynolds from the University of Arizona, while municipal water supplies are generally safe, contaminants can enter water bottles through our hands and saliva. She notes, “The water bottle itself is just the perfect environment for bacteria to grow. It’s like a little incubator.”
Maintaining cleanliness in your water bottle hinges on your hygiene practices, which might not be as straightforward as one would think. For example, a study showed that out of 30 participants, 27 refilled their bottles without washing them.
So, what do the experts suggest?
How to clean your reusable water bottle
Start with clean hands – and don’t forget your phone: Before tackling the bottle, ensure your hands are clean.
Reynolds emphasizes that “the source of the water bottle’s contamination is probably your hands.” But frequent washing won’t help much if you’re not also cleaning your phone regularly. Wiping it down with a cloth slightly dampened with soap and water at least once a week is recommended, as cell phones often harbor many germs. Research shows that around 68% of phones are contaminated with some sort of microorganism.
Use soap, bleach, or vinegar: Simply rinsing your water bottle with water won’t cut it, as Reynolds explains; that’s insufficient for eliminating biofilm. You can use a diluted bleach solution in the sink or dishwasher. Just fill the sink with water, add a capful of bleach, and let the bottle soak for a minute or so. Afterwards, make sure to rinse it thoroughly. Be careful, though—use gloves and never mix bleach with other cleaners.
Alternatively, basic dish soap works well too. Scrubbing with a brush helps eliminate any crevices where bacteria thrive. However, anti-microbial soaps should be avoided; they can contribute to antibiotic resistance.
Cleaning with vinegar can also help reduce biofilm, according to another expert, Kellogg Schwab.
If you decide to use a dishwasher, check that your bottle is marked as “dishwasher-safe.” Just a heads-up: washing plastic in the dishwasher might release microplastics.
Hot water is preferable: While the difference between hot and cold water might be subtle, using hot water is usually better for achieving soap lather. This lathering time can actually enhance the effectiveness of the wash.
Pay attention to the lid and straw: These components are often the most contaminated, as they can trap moisture, making it easier for microbes to flourish. Using a bottle brush specifically for these spots is a good idea.
Let it dry completely: Ensuring your bottle is dry can deter bacterial growth, as Reynolds points out.
Regularly wash your bottle: Aim to wash your bottle daily if possible. “You wouldn’t eat out of the same dirty cereal bowl every day, so why drink from a dirty water bottle?” Reynolds asks.
Environmental conditions play a role in contamination, too. For instance, leaving a bottle in a hot car can accelerate bacterial growth.
If you can see or smell something, it’s too late: While bacterial growth won’t harm you immediately, it can lead to the formation of a slimy substance known as biofilm. Schwab explains that signs of biofilm can affect taste and smell. A musty odor can emerge that’s definitely unpleasant.
If biofilm persists, it can become visible, similar to mold in a shower. However, if you can see it, you might be dealing with a concerning number of microorganisms—sometimes as few as a hundred can make you ill.
“If you can see or smell biofilm, you have way too much already,” Schwab warns. “That’s not a hygienic situation.”
While bacteria make up the majority of biofilm, there’s also the possibility of fungi, algae, and viruses.
Choose your bottle carefully: According to Schwab, metal and glass water bottles tend to inhibit bacterial growth more effectively than plastic ones. Regardless of what your bottle is made of, consistent cleaning is essential. “Eventually, bacteria can exceed a threshold in any material,” Reynolds states.
What happens if you don’t clean your bottle?
Bacteria can thrive in the moist environment of a water bottle. For instance, under optimal conditions, E. coli could double its population every 20 minutes.
Reynolds’ team recently surveyed individuals at a water refill station to see if they would permit microbial testing of their reusable bottles. While results aren’t published yet, preliminary findings indicate that while refill station water is generally clean, many bottles contained residual water that was not. Approximately half of the samples showed bacterial contamination, with 10% containing E. coli.
In Reynolds’ recent study on various water sources, levels of E. coli were lower in bottles cleaned with soap and water compared to those rinsed only with water.
Drinking water tainted with E. coli can lead to symptoms such as stomach cramps and nausea. While the threat of severe illness is typically low, Reynolds insists that “routine maintenance is simply good hygiene.”
Cleaning is especially crucial if you’ve been ill, as it’s easy to transfer pathogens back to yourself. Although some organisms can build immunity, properly cleaning the bottle before reuse is always best practice.
