Another Goron wants to drink it before it clears some rocks. But you can't get him his water before the shop in Castle Town is reopened.... for which you have to get the first Goron his barrel of hot water. It's annoying with the enemies attacking you or the barrel.... just put it down (grab your bow) and shoot the suckers before they come close.
Oh btw, how much time did you play before you beated the game? 55 hours here. I'm now clocked almost at 60, I just run around a lot trying to find stuff.