When I look at the "Hydration" section of a ride in Garmin Connect, it looks like it's telling me how much fluid (in cups) I drank on the ride, and a percentage of what I should have drunk (also in cups) based on estimated fluid loss (presumably taking into account duration, temperature, effort, power output, etc.). I can certainly understand how the Garmin could estimate fluid loss, and therefore how much fluid I should drink, but how on earth could it possibly estimate how much I've had to drink during the ride?
It seems eerily accurate on the rides it's measured (I think this is a new feature in firmware v. 8.0.0), within a cup or two of what I actually drank.
