I am going to say this once and then be quiet. During my escape and evasion exercise in 1963, some of my comrades were water boarded to show what it would be like and its affects. They all survived. At that time, it was not considered "torture" but a very effective interogation method. Times and attitudes have changed but that does not relieve the usefulness of a technique of interogation no longer acceptable because we might hurt an enemy's psyche.
How long were they subjected to it? Many of the detainee's endured it for hours at a time. Like anything you can do it once and survive, repeated use can lead to ill effects.