Getting Answers: bacteria found in reusable water bottles

Researchers at Quinnipiac University in Hamden, CT recently took a look at what may be growing in your favorite cup.
Published: May. 24, 2023 at 9:03 AM EDT
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(WFSB/WGGB/WSHM) - When was the last time you washed your reusable water bottle or the straw inside? It’s something that a lot of people maybe don’t think about. Researchers at Quinnipiac University in Hamden, CT recently took a look at what may be growing in your favorite cup.

During a visit at Quinnipiac’s student center, 30 reusable water bottles were swabbed. The students who had their water bottles tested had a feeling there might be some bacteria growing.

“I know it’s gross because I don’t really wash it, but I only put water in it,” said student Olivia Chomick.

“Oh you might find some stuff in there, yeah. I feel like it’s pretty gross because like when you’re living on a college campus you don’t get to wash things that often,” said student Devandra Chin.

Each water bottle was swabbed twice: once on the inside and once on wherever you would put your mouth.

The swabs then went over to a lab at Quinnipiac’s Buckman Center. Microbiology laboratory manager Donnasue Graesser led her students through the testing process. Each swab was tested two different ways.

A recent study from found on average a reusable water bottle had 40-thousand times the bacteria of a toilet seat.

Six days after the initial testing, researchers explained what they found.

“They all grew bacteria. They all grew quite a bit,” said medical microbiology major Matthew Pinsley.

Pinsley analyzed the results. He says all the swabs grew bacteria which isn’t surprising considering how much bacteria is in your mouth.

However, it wasn’t just mouth bacteria that they found.

“This one actually inhabits soil, so that means soil or dirt is getting into our bottles,” said Pinsley.

Pinsley found bacteria from the throat, soil water and other places that could not be categorized.

Around 30% of the swabs also had fecal matter.

“I think it is indicative of how sanitary we are, that we are finding bacteria that is in our stool on our water bottles,” said Pinsley.

Can any of that bacteria make you sick? Well, it depends.

“To immuno-competent people, not necessarily. Although it is indicative that norovirus is present,” said Pinsley.

Pinsley says they didn’t find any significant differences between plastic versus stainless steel bottles. Straw cersus no straw also didn’t seem to impact results.

Chin was shown the bacteria her swabs grew. Her bottle did not have fecal matter on it, but the 30% number still concerns her.

“That’s shocking, like that’s a lot. How does that even get there?” said Devandra Chin. “That makes me want to wash it right now.”

A report from Michigan State University suggests washing your bottle at the end of every day and taking the extra step to sanitize it once a week. You can sanitize your bottle by sticking it in the dishwasher. If that’s not an option, you can use a weak bleach solution. The report also suggests not letting water sit in your bottle for long periods.