dehydration

Even after a short session (around 1hr) I get so dehydrated I need 3+ liters of water just to feel normal. Basically I can't do any higher thinking for the rest of the day 
I try to get an intake of liquid before I go into the water, and right after surfing.
Male,35, recent bloodwork came back normal.
Is this how it is for everyone? I can't imagine a daylong session.

I try to get an intake of liquid before I go into the water, and right after surfing.
Male,35, recent bloodwork came back normal.
Is this how it is for everyone? I can't imagine a daylong session.