Point: Water boarding as it is currently described involves strapping a person to an inclined board, with his feet raised and his head lowered. The interrogators bind the person's arms and legs so he can't move at all, and they cover his face. In some descriptions, the person is gagged, and some sort of cloth covers his nose and mouth; in others, his face is wrapped in cellophane. The interrogator then repeatedly pours water onto the person's face. Depending on the exact setup, the water may or may not actually get into the person's mouth and nose; but the physical experience of being underneath a wave of water seems to be secondary to the psychological experience. The person's mind believes he is drowning, and his gag reflex kicks in as if he were choking on all that water falling on his face.
Counterpoint: When the CIA used the water-boarding technique on al-Qaeda operative and supposed "9/11 mastermind" Khalid Sheik Mohammed, he reportedly lasted more than two minutes before confessing to everything of which he was accused. Anonymous CIA sources report that Mohammed's interrogators were impressed.