In a recent Vanity Fair article, the author undergoes the procedure at the aid of people who train US military to RESIST (not inflict) this horrendous "enhanced interrogation" technique.
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On a personal note, as I've probably stated before, people seem to focus on the "well they aren't actually drowning, so it's not torture" aspect of it.
Psychological trauma is even more debilitating than physical, and even if there is no true risk of drowning (which this article disputes, as they stated there were no guarantees he wouldn't suffer injury or death) the person being subjected to this abominable act of dominance and abuse would be quite potentially psychologically scarred from this experience.
If this act happened under any other circumstances outside the fog of the war on terror, it would be immediately called for what it truly is.