Edge play is dangerous; do not try this at home!
Waterboarding is a form of torture, more specifically a type of water torture, in which water is poured over a cloth covering the face and breathing passages of an immobilized captive, causing the individual to experience the sensation of drowning. Waterboarding 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, and death. Adverse physical consequences can manifest themselves months after the event, while psychological effects can last for years. Penalties in some regions for using this technique can constitute charges of war crimes and treason.
In the most common method of waterboarding, the captive's face is covered with cloth or some other thin material, and the subject is immobilized on his/her back. Interrogators pour water onto the face over the breathing passages, causing an almost immediate gag reflex and creating the sensation for the captive that he is drowning. Victims of waterboarding are at extreme risk of sudden death due to the aspiration of vomitus. Vomitus travels up the esophagus, which can then be inhaled (mostly into the right lung due to its more direct pathway).
The United States' Office of Legal Counsel in August 2002 responded to the request by the CIA for a legal opinion regarding the use of certain interrogation techniques. It included the following account of the CIA's definition of waterboarding in a Top Secret 2002 memorandum as follows:
In this procedure, the individual is bound securely to an inclined bench, which is approximately four feet by seven feet. The individual's feet are generally elevated. A cloth is placed over the forehead and eyes. Water is then applied to the cloth in a controlled manner. As this is done, the cloth is lowered until it covers both the nose and mouth. Once the cloth is saturated and completely covers the mouth and nose, air flow is slightly restricted for 20 to 40 seconds due to the presence of the cloth... During those 20 to 40 seconds, water is continuously applied from a height of twelve to twenty-four inches. After this period, the cloth is lifted, and the individual is allowed to breathe unimpeded for three or four full breaths... The procedure may then be repeated. The water is usually applied from a canteen cup or small watering can with a spout... You have... informed us that it is likely that this procedure would not last more than twenty minutes in any one application