Clean your water bottle more (and properly!) You are almost certainly not doing it enough. At the very least, you gotta let that thing air dry between uses to avoid bacteria and mold growth (and a bad taste).

Here are some best practices for cleaning your bottle:

• To properly clean a water bottle, wash daily with hot, soapy water and a bottle brush, focusing on the lid and straw, then let it air dry completely; for deep cleaning weekly, use a solution of hot water with vinegar, baking soda, or denture tablets to sanitize and deodorize, scrubbing nooks and crannies, and rinsing thoroughly before drying.
• Daily Cleaning (Quick Wash)
• Disassemble: Take off the lid, straw, and any other parts.
• Wash: Use hot water and a few drops of dish soap with a bottle brush to scrub the inside, outside, lid, and straw (use a pipe cleaner for straws).
• Rinse: Rinse all parts thoroughly with warm water.
• Dry: Air dry all pieces upside down to prevent moisture buildup.