I used to think much like the original poster, believing that a water bottle didn’t really get dirty if it only contained water. However, after some research and personal experience, I realized this isn’t the case. Even though water itself is clean, bacteria and mold can still accumulate inside bottles, especially if they’re not washed regularly. Moist environments are perfect breeding grounds for microorganisms that can cause unpleasant smells, tastes, and even potential health issues. Cleaning your bottle at least once a week, or more often if you use it daily, helps prevent this buildup. In my experience, using a simple bottle brush with warm water and mild soap does the trick. For deeper cleaning, especially for bottles with narrow openings, a mixture of baking soda and vinegar or specialized cleaning tablets can be very effective. Rinsing thoroughly afterward ensures no residue remains. Aside from health reasons, a clean bottle simply tastes better. I noticed a significant improvement in the flavor of my water when I started keeping my bottle clean, which encouraged me to drink more water throughout the day. In summary, even if your bottle holds "just water," regular cleaning is a must for hygiene, taste, and your overall health. It only takes a few minutes, and the benefits make it well worth the effort.