Overhydration, but I'm not sure whether a sedentary person drinking it orally is at risk for that. (We know runners drinking hydration fluid and sedentary people taking hydration intravenously are at risk).
Empty calories, but you can offset that.
Excess salt (but it is now uncertain as to whether excess salt is harmful in the absence of high blood pressure).
It's also weird, as in it's both an evolutionary novel and culturally novel thing for you to do, and that means it's risky until proven innocent.
This thread is for asking any questions that might seem obvious, tangential, silly or what-have-you. Don't be shy, everyone has holes in their knowledge, though the fewer and the smaller we can make them, the better.
Please be respectful of other people's admitting ignorance and don't mock them for it, as they're doing a noble thing.
To any future monthly posters of SQ threads, please remember to add the "stupid_questions" tag.