Alrighty which jerk designed the human body so that it has a state of dehydration where you suffer no noticeable side effects except that your brain goes "water? Pffff who needs it? Squares, that's who. You're fine!!" Until you actually decide "huh it's been a while since I drank any fluids, I'll just have a small glass of water since it's hot" and your brain suddenly goes "I NEED IT I'M A SQUARE GIVE ME THE SPLASHY STUFF OH MY GOD"

And then...

Bladder: "just as planned...!"