Water bottles can harbour nasties if not kept clean. Remember to empty and wash your reusable water bottles daily after use to prevent bacteria, and even fungi, growing inside the bottle from it touching your mouth or even leaving a half-finished bottle lying about at room temperature. Use hot water and a bottle brush then allow the bottle to air dry thoroughly before refilling or put it in the dishwasher if the bottle is dishwasher safe. If you use a water bladder when jogging or cycling you can clean it with hot water and two tablespoons of baking soda or bleach, hold the bladder up and pinch the bite valve so the solutions runs into the tube, then leave for 30 minutes. Then rinse with clean water. Some brands also sell cleaning tablets to use