What is it, exactly?
The technique was characterized in 2005 by former CIA director Porter J. Goss as a "professional interrogation technique", [and] involves tying the victim to a board with the head lower than the feet so that he or she is unable to move. A piece of cloth is held tightly over the face, and water is poured onto the cloth. Breathing is extremely difficult and the victim will be in fear of imminent death by asphyxiation. Journalists Brian Ross and Richard Esposito described the CIA's waterboarding technique as follows:
The prisoner is bound to an inclined board, feet raised and head lightly below the feet. Cellophane is wrapped over the prisoner's face and water is poured over him. Unavoidably, the gag reflex kicks in and a terrifying fear of drowning leads to almost instant pleas to bring the treatment to a halt. According to the sources, CIA officers who subjected themselves to the water boarding technique lasted an average of 14 seconds before caving in. They said al Qaeda's toughest prisoner, Khalid Sheik Mohammed, won the admiration of interrogators when he was able to last over two minutes before begging to confess.
NOTE: The "confessions" thus extracted from Khalid Sheik Mohammed (and from Ramzi Binalshibh) are practically the only "evidence" ever adduced against the 19 alleged hijackers of September 11th. We are expected to take it on trust that they made such confessions, and that such confessions are credible. No one outside of the US military has ever seen either of these two men since their alleged arrests.