If you have a reusable water bottle, then you have to disinfect it regularly. It's not enough just to rinse it out. You need to soak it overnight with vinegar. Then wash it with dishwashing liquid and water the day after. If you never clean your bottle properly then it can grow a toxic mold and make you very sick. It's best to have a clear or see-through bottle instead of a tinted one. Then you can see what's going on in there.