>>538096818
Sugar-free artificial flavor concentrate- mainly citric acid and an artificial flavor. Some of them have added caffeine or other "healthy" additives.
>>538096682
You'd need to drink a bottle of the stuff raw for it to kill you (expired or not)- something else probably killed the guy, but it's still very funny that he tweeted about "finding out the hard way that water enhancers can expire", then tweeted about being deathly ill, and finally died. It's significantly more likely that he had other issues and attributed it to expired Mio instead of his shit lifestyle.
For reference: 1 squeeze = ~60mg caffeine, intended for 12oz diluted volume