You don’t buy plastic water bottles to be kind to the environment. But your reusable water bottle may be teeming with bacteria that’s not exactly healthy, either. The most popular and effective water bottles are vacuum insulated to keep water at a regulated temperature and more palatable for hydration.

According to research, about 75% of Americans are chronically dehydrated. That’s why having a water bottle on hand is so important.

But reusable water bottles must be kept scrupulously clean to avoid malodorous water that could cause illness, says NBC News. The first rule of water bottle hygiene is to clean it thoroughly every day. “Standing water is never good in a water bottle,” says Dr. Sharon Nachman, a pediatric infectious disease expert from Stony Brook University. If water sits too long in a bottle at the right temperature, it can grow bacteria.

To properly clean the water bottle, remove all existing liquid. Mix lukewarm water with a mild dish soap and pour it into the bottle. This helps destroy microbes because dish soap contains surfactants that trap dirt and remove it from the surface of the bottle. Don’t use cold water because it hinders the soap from dissolving and doing its job. You can also use distilled white vinegar, or baking soda to effectively clean water bottles. Use a small, bristled cleaning brush instead of a sponge to get into all the nooks and crannies.

Once you’ve cleaned the bottle with whatever product you selected, rinse it out and allow it to dry.

Avoid eating and using your water bottle to drink, say experts, who reveal that the bacteria from your mouth after eating can transfer into the water and cause a telltale smell.

Nachman does not recommend putting water bottles in the dishwasher as these appliances use powerful detergent pods that may damage your bottle. However, there may be some benefit to running the bottle through the dishwasher if it has a sanitize cycle that kills germs with high heat.

Bottom line: Clean your water bottle daily for the best-tasting, healthiest and safest hydration.