Whether you are going to the gym or you work a desk job, staying hydrated is important. Keeping a reusable bottle of water is usually what people have to do so.

You might want to think twice before doing that.

According to a study by Treadmill Reviews, reusable water bottles contain high levels of human-harming bacteria. Swabbing four different bottle styles, the study found the containers were crawling with more than 300,000 colony-forming bacteria units per square centimetre.

Conclusion: drinking from a refillable bottle may be worse than licking a dog’s toy, the U.K. Sun reported.

The study detected that the average water bottle had 313,499 CFU (colony-forming units of bacteria) compared to 2,937 CFU found on a dog’s toy.

Bottles with a slide-top spout contained the most germs with an average of 933,340 CFU.

Squeeze-top bottles are just as harmful with an average germ count of 161,971 CFC.

Screw-top lid bottles aren’t as bad with 159,060 CFU. Surprisingly, the least harmful were straw-top bottles with a fraction of an average compared to others at just 25.4 CFU.

While squeeze-tops weren’t as harmful as its slide-top counterparts, almost 99% of bacteria found on the bottle contained harmful traces of antibiotic-immune bacteria like E.coli, the study suggested.

Overall more than 60% of germs found on water bottles can make people sick.

The study’s researchers suggested using straw-tops or stainless steel bottles over plastic ones. Researchers also recommend not letting a half drunk bottle sit unattended for weeks.

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Bottles should also be hand washed with a weak bleach solution or cleaned via dishwasher.