Understanding Reusable Water Bottles

Using a reusable water bottle is a wise choice. It helps save money, reduces single-use plastics, and keeps us hydrated. But there’s a downside that many of us might not consider.

Most people don’t clean their bottles as thoroughly or frequently as they should, which means germs can linger on the surfaces we touch.

As of 2024, the reusable water bottle market was estimated to be around $10 billion, with surveys showing university students report using them between 50% to 81% of the time.

A study at Purdue University closely examined daily habits to see just how clean these bottles really are. The findings might surprise you, but they also suggest some easy changes we can all make.

Research Findings on Reusable Bottles

The research aimed to answer a straightforward question: “How clean are the bottles that students regularly use?”

To gather real data, researchers collected 90 bottles from students. They asked the owners about their cleaning habits and then tested the bottles in two different ways.

First, they used a quick hygiene test called ATP on the outer surfaces, which detects organic residues. This method is commonly employed in food safety to verify cleanliness after washing.

Next, they rinsed the inside of the bottles and counted the bacteria on water-contact surfaces, including common water-loving bacteria and coliforms, which can indicate more serious contamination issues.

This study was led by Carl Behnke at Purdue University, assisted by various academics, including Dr. Yuriko Fukuta from Baylor College of Medicine, who added medical insights.

The intention wasn’t to criticize anyone’s bottle; it was to correlate daily cleaning habits with actual cleanliness, allowing people to adjust their behaviors accordingly.

Exterior Cleanliness

The outside of the bottles turned out to be dirtier than many expected. The ATP test indicated that all collected bottles (including two new ones from a store) were deemed “dirty.”

That’s understandable in our daily routine, where hands transfer bacteria from phones, doorknobs, and keyboards to bottle caps. Anything left behind provides a hub for germs to thrive.

More refills corresponded to dirtier exteriors, as each refill introduces new touchpoints: hands, the cap, counters, and faucets. The rim is significant here since it connects hands and mouths.

Inner Cleanliness

The research also explored the interior of the bottles to measure how many bacteria were present. The results were alarming: many bottles contained higher bacterial counts than what is generally deemed safe for drinking water.

Most guidelines suggest keeping drinking water below 100–500 CFU/mL. In this study, about 70% of the bottles tested below 100, while many exceeded 500. Simply put, most bottles contained more bacteria than is safe for consumption.

Researchers also examined coliforms, which signal sanitation issues. The norm for bottled water should be none detected; however, approximately 25% of the bottles failed this standard.

Bacteria require moisture, nutrients, and time to thrive. Water bottles, by nature, provide moisture, and any non-water contents could become feeding grounds for bacteria.

Interestingly, bottles used solely for water showed lower bacterial levels, while those that also held sugary or creamy beverages had significantly higher counts.

Cleaning Practices

The material of the bottle played a minor role in cleanliness. Glass bottles often appeared cleaner, likely due to their smooth, non-porous surface. However, no material is exempt from proper care.

Design factors—like narrow openings or multiple parts—can create hidden spaces where residue accumulates. A general pattern emerged: more frequent cleaning usually resulted in better results, though intentions didn’t always translate into practice.

A simple rinse may leave bacteria behind, and dishwashers might not adequately clean all areas of the bottle.

Behnke pointed out, “We wash our dishes regularly but often neglect our bottles,” highlighting the need for more effective cleaning habits.

Health Implications

Fukuta raised concerns that the bacteria found could include staphylococcus or strep. The study found that over 20% of the bottles contained coliform bacteria, which suggests fecal contamination.

A dirty bottle can act as a carrier for microbes, especially since hands touch the cap and rim, making it easy for germs to be transferred to the drinking surface.

“We’re constantly touching our water bottles with our mouths and hands,” Dr. Fukuta noted. “This can lead to sickness, particularly for those with weakened immune systems.”

Tips for Keeping Reusable Bottles Clean

Think of your reusable bottle like a food-contact surface. Use hot water and dish soap, and give it a thorough scrub with a bottle brush.

Don’t forget to clean nooks using a small brush or toothpick and to take apart lids, straws, and other components for a more complete clean.

Ensure everything dries completely with the cap off to eliminate moisture that encourages bacterial growth and prevents musty odors.

If you drink sweetened beverages, make it a point to clean your bottle the same day. If your bottle has lots of parts that you tend to skip cleaning, a simpler design might encourage better habits.

It’s best to avoid sharing bottles, as saliva can introduce new microbes that may cause issues later on.

If your bottle frequently sits on public surfaces, it’s a good idea to clean the exterior often, especially the rim and cap.

Conclusion

While reusable bottles are still a practical and sustainable choice, they do require consistent cleaning. Their interiors aren’t sterile, and the exteriors can pick up residue quickly. Pair regular use with a solid cleaning routine, and you can return your bottle to its intended role: a safe hydration tool instead of a vessel for germs.

The full study was published in the journal Food Protection.