Those refillable water bottles may be good for the environment, but they may be bad for your health.
A new study found they contain more bacteria than your dog's bone.
A team from the website treadmillreviews.net swabbed the lids of 12 water bottles used by athletes, each bottle contained about 1,000 times more bacteria than an average dog toy.
The study showed water bottles with a straw top were the cleanest, while slide tops were the germiest.
Experts said you probably won't get sick from your water bottle, but it is important to wash it regularly.