Dirty water bottle, healthy gut? FGCU biologist explains why sterile isn’t safer

LEE COUNTY, Fla. —

When was the last time you washed your reusable water bottle?

"I wash it once a week. Yeah, once a week before I have to leave for my Monday classes," said Florida Gulf Coast University sophomore Sophia Uliani.

It's safe to say the answer varies depending on who you ask.

"I have some friends who wash it every day. Like, as soon as they come home from school. But then I have some friends, and they're like, 'Oh, I feel like three months is fine. So we have a very wide variety of what we think is clean," Uliani said.

And if you ask FGCU biology professor Dr. Nora Demers, she'll tell you it doesn't really matter how often you wash your water bottle.

"I hardly ever wash mine," she said.

Demers and Uliani did an experiment to see what's living on our water bottles. We swabbed some places you might expect to have a lot of bacteria, including a cellphone and the bottom of a shoe. Then, we swabbed a water bottle that gets washed maybe once a month and another one that was washed the day before.

"And then we also swabbed natural areas like our trees, our leaves, and our dirt. We're just trying to see a comparison of things that are supposed to seem sterile, like the bench, right? You're going to probably wipe it down for your kids because like, oh, there's bacteria on there," Uliani said.

We put each sample into petri dishes with different food sources.

"Then we put it in an incubator for a couple of days, and we had it set for normal body temperature," Uliani said.

That gave the bacteria, that's typically invisible to the naked eye, a chance to grow so we could see what's really there.

The water bottle that hardly ever gets washed had a lot of diversity, and Demers is on a mission to prove that's actually a good thing and set the record straight on bacteria.

"I don't think it's a problem. The stuff that's growing on the bottles that are not washed is the same stuff that's on my tongue, and it belongs there. It's not going to do any harm as long as you're healthy, nutritionally sound, and you haven't got a cut or something," Demers said. "We, animals, have been living with bacteria for probably a couple of billion years or more. And we've evolved together."

She and Uliani pointed out some ways that good bacteria protect us.

"Bacteria in our gut are helping our are helping us digest our food. We can't really digest much vegetable roughage at all. But because we have bacteria in our gut, they digest it for us and give us the food directly," Demers said.

There's a mix of different bacteria living all over us and within us, from our eyes and brain to our genitals and skin.

"Our very first line of defense against disease is a thin layer of bacteria that grows on our skin," Uliani said.

They also point to research that shows creating an environment that's too sterile can actually make you sick.

"You're hearing about all the cases of eczema that are going on. It's not just because of the diagnosis. It is because we are changing the way the world around us exists," Demers said. "So lupus, eczema, asthma, psoriasis, all of these commercials that you're seeing on TV for all these different medications that we're having an autoimmune response to, because when we were young, we were not exposed to these things in a natural way."

You may know this as the hygiene hypothesis, which points to cleaner environments and less exposure to infections, increasing health risks. It even suggests that reduced exposure to fecal bacteria can be linked to immune system dysregulation.

"You can absolutely swallow, poop, and not get sick. And we now use it as medicine," Demers said.

She said there are absolutely bacteria that will make you sick, but the real problem is when it gets into places it's not supposed to be, like your bloodstream.

"That's why a tattoo artist has sterile instruments, right?" she said.

But she insists bacteria on your water bottle shouldn't be a big concern.

"And you can save a ton of money. Think about how much money you can save if you stop trying to make your world sterile. You know, somebody is selling you a bill of goods to tell you bacteria are bad. This (experiment) is showing you they're all around you, and none of us are sick. Somebody taught us to say 'ew' instead of 'wow,'" she said.

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