We've all been told that to keep hydrated, the best drink is always water, and we should consume at least 64 ounces per day. Conversely, to keep from dehydrating, the standard advice is to avoid caffeinated beverages because they're diuretics that cause you to lose water. Ditto for alcohol.
Unfortunately, most of the things we thought we knew about healthful hydration no longer seem to be certain.
For example, the advice to drink at least eight 8-ounce glasses of water per day turned out to have very little evidence supporting it. The idea that coffee and other caffeinated beverages dehydrate you also seems to be incorrect, given the conclusions of this meta-analysis that any concerns "regarding unwanted fluid loss associated with caffeine consumption are unwarranted."
So what should you really be drinking to stay hydrated?