http://en.wikipedia.org/wiki/Waterboarding
Waterboarding is a form of torture which consists of immobilizing the victim on his or her back with the head inclined downwards, and then pouring water over the face and into the breathing passages, causing the captive to believe he or she is dying.
Forced suffocation and water inhalation cause the subject to experience the sensation of drowning. Waterboarding is considered a form of torture by legal experts, politicians, war veterans,medical experts in the treatment of torture victims, intelligence officials,[9] military judges[10] and human rights organizations.[11][12]
In contrast to submerging the head face-forward in water, waterboarding precipitates an almost immediate gag reflex.[13] While the technique does not inevitably cause lasting physical damage, it can cause extreme pain, dry drowning, damage to lungs, brain damage from oxygen deprivation, other physical injuries including broken bones due to struggling against restraints, lasting psychological damage or, if uninterrupted, death.[3] Adverse physical consequences can start manifesting months after the event; psychological effects can last for years.[7]