Apart from cleaning water bottle daily with hot water, a bad odor always remains.
Are these some kind of bacteria harmful to our health? How to get rid of this bad odor and have a fresh smell from water bottle? Is this bad odor negligible?
In addition to Paparazzi's obvious but necessary "clean them in warm soapy water" periodically...
We get the same thing with re-usable SodaStream bottles which are only ever plain water, fizzed.
If you have a smell that still hangs around after washing properly, then try filling with a solution of Bicarbonate of Soda & let stand overnight. Leave the lid off, it can be a bit fizzy.
Then, to prevent it in the first place, always leave the lid off once it's empty.
Lid off allows the bottle to dry out between uses. You don't really want stagnant water sitting around for too long.
What I have always done is once a month or so I rinse my water bottle with white vinegar then soap and water to get the vinegar smell out. The vinegar kills all those bacteria that sink into the small crevices that are too small for the human eye to see. It is also best to leave the lid off when you have finished drinking the water as to let the rest of the water evaporate and not become stagnant.