If you don’t wash your bottle frequently enough, you could get sick more often, says Tony Kim, Ph.D., assistant professor at James Madison University in Harrisonburg, Virginia. In a study he co-authored last year, he looked at the germs in 90 reusable bottles and found that coliform bacteria like E. coli, which can cause stomach bugs, was among the most common.
Coliform and other strains are more likely to breed if there’s saliva (from backwash) present or if you keep your bottle at room temperature, like on your desk, throughout the day. It’s even worse if you drink out of an opaque container since the inside is dark and moist, prime conditions for bacterial growth.]
Rinsing, even if you use soap, doesn’t do much. To really get rid of bacteria, you need to scrub the bottle’s inside as well as its mouthpiece, straw, and top, Kim says. Ideally you’d wash yours using a brush or sponge with a bleach-based cleaning product every time you drink a bottle-full and let it air dry pre-refill—even if that means multiple times per day.
At the very least, always dump out leftover H2O to remove some of the germs left behind by your saliva. Better yet, invest in a self-cleaning bottle like LARQ that will do the work for you.