Great cup. We have two, one for water, the other for milk. Some ppl complain it leaks, that's because the lid is not put on right. I check it every time after I put the lid on by shaking the cup upside down. If it leaks, I unscrew it and put it back on again. I lost the o-ring one time, emailed Zoli and they sent one in the mail to me for free.