I put stuff in mine. NUNN lately. Sometimes gatorade mix. If I have anything besides plain water in it, it gets a denture tablet when I get home and a good rinse. I used the same bladder for 5 years doing that without a problem or funky odors. It finally sprung a leak, but I doubt that was related to putting flavored drinks in it. I figure 5 years with the same plastic bladder is long enough...