How do you clean a water bottle that smells?

Fill the bottle with a mixture of one tablespoon of baking soda and warm water, shake vigorously, and let it soak overnight. For stubborn odors, use a mixture of white vinegar and water (1:4 ratio) instead. Rinse thoroughly and let it air dry completely with the cap off. For bottles with straws or complex lids, use a bottle brush and pipe cleaners to reach hidden crevices where bacteria and mold can grow.