You may have read by now the official lie about this treatment, which is that it “simulates” the feeling of drowning. This is not the case. You feel that you are drowning because you are drowning—or, rather, being drowned, albeit slowly and under controlled conditions and at the mercy (or otherwise) of those who are applying the pressure. The “board” is the instrument, not the method. You are not being boarded. You are being watered. This was very rapidly brought home to me when, on top of the hood, which still admitted a few flashes of random and worrying strobe light to my vision, three layers of enveloping towel were added. In this pregnant darkness, head downward, I waited for a while until I abruptly felt a slow cascade of water going up my nose. Determined to resist if only for the honor of my navy ancestors who had so often been in peril on the sea, I held my breath for a while and then had to exhale and—as you might expect—inhale in turn. The inhalation brought the damp cloths tight against my nostrils, as if a huge, wet paw had been suddenly and annihilatingly clamped over my face. Unable to determine whether I was breathing in or out, and flooded more with sheer panic than with mere water, I triggered the pre-arranged signal and felt the unbelievable relief of being pulled upright and having the soaking and stifling layers pulled off me. I find I don’t want to tell you how little time I lasted.
Believe Me, It’s Torture - Christopher Hitchens on Waterboarding