Just how dirty is your reusable water bottle?

Many people have reusable water bottles because it’s cheaper and better for the environment than buying single-use plastic bottles — not to mention the viral fixation behind water bottles like the Stanley Cup tumbler. But the reality is that many people don’t wash them regularly with soap and water.

Scripps News Indianapolis' investigative team gathered up half a dozen water bottles made of varying materials and took them to a microbiology lab at the Indiana University School of Medicine.

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"I study bacteria and how they cause infection,” said Indiana University assistant professor Jay Vornhagen.

Our hands and mouths carry germs, which can end up on our water bottles.

“If you're not cleaning them properly, there's a chance they could make you sick,” said Vornhagen.

The different bottles were labeled and swabbed by Vornhagen, a graduate student and a research analyst. They also added one of their own water bottles.

“We included what we call a control in this experiment,” said Vornhagen. “We actually took a water bottle and put bacteria on that water bottle."

Vornhagen and his team tested for germs and pathogens, which are organisms that can produce diseases.

“We will know everything a week from now,” said Vornhagen.

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A week later, the team returned to the lab for the results.

"We have bacteria on all the water bottles you brought us,” said Vornhagen. “Most of it is good bacteria."

The good news: 5 of the 6 water bottles tested did not contain any bacteria that can make you sick. But one of the cups did come back with some concerning results.

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“We found a couple of pathogens that are interesting,” said Vornhagen. “One is staphylococcus, it's like MRSA."

Staph infections, caused by staphylococcus, can impact the skin, bones, digestive system, lungs and bloodstream.

Vornhagen had a hairy take on how staphylococcus got onto the Stanley tumbler, which belonged to one of the team's young children.

“That bacteria similar to MRSA we usually think of it as being associated with dogs,” said Vornhagen. “If you have a dog that's interacting with the water bottle, sometimes the bacteria from the dog's mouth can get in and on those spaces."

But that wasn't all the researchers found on the kid’s water bottle.

“This is what we call coliform bacteria,’ said Vornhagen. “Coliform are those bacteria that we worry about causing you to get sick. We think of them coming from the gut."

In other words, poop.

“It happens, right?” said Vornhagen. “We have lots of different illnesses that pass through the fecal-oral route, we get some sort of fecal contamination, it goes into our water."

But wait, there's more.

“Sometimes those poop bacteria can be really drug-resistant and the antibiotics to kill those bacteria,” said Vornhagen. “In this case we did find some examples of antibiotic-resistant bacteria.”

So where did all these bacteria come from?

Vornhagen suspects the water bottle was brought into a bathroom or locker room setting.

“Just one more reason to keep the water bottles out of bathrooms and away from toilets and things like that,” said Vornhagen.

As for the "control" water bottle researchers added to the test, Vornhagen showed the difference before and after it was washed with warm soap and water.

“As you can see, after that wash, there is no bacteria after a wash,” said Vornhagen. “That says warm water and soap is sufficient to clean a water bottle to get rid of potential pathogens. You don't need to do anything more."

Vornhagen points out that most of the time, you’re getting sick from other people, not from the germs on your own water bottle. Certain groups of people could be more impacted by a dirty water bottle than others.

"If you're immunocompromised or you're old, that is something to be concerned about, it could make you sick,” said Vornhagen.

Experts recommend washing your water bottle daily and also doing a deep clean once a week, which should include taking apart the water bottle and washing all the pieces.

You should also prioritize washing with soap and water if you’ve had anything with sugar in your water bottle.

This story was originally published by Kara Kenney at Scripps News Indianapolis .