If you’re not washing it, then yeah, it can get kind of gross. Reusing an unwashed bottle or cup, even if you’re “only” drinking water out of it, puts your mouth in intimate contact with a wonderful bacterial breeding ground.
Bacteria grow really well in moist, warm environments. While almost any similar container will suffice, a narrow-mouthed plastic water bottle is difficult to scrub and especially friendly to bacterial growth. In a 2003 study, Canadian researchers collected samples from... READ ON