Although realism is important, there are concessions that need to be made. Just drink the 3 bottles and be happy you don’t have to sip water every 20 minutes like in real life. The more realistic “water sipping” would be too awkward to quantify and too tedious to deal with for the player.
I thought about it too when I downed 3 bottles of water in one sitting, but I’m glad I can do that rather than having to drink water every 20-30 game minutes.