After covering this nightmare for many years, I can only urge you to read Philip Zelikow's take. He saw what was going on from the inside and this point is essential:
1. The focus on water-boarding misses the main point of the program.
Which is that it was a program. Unlike the image of using intense physical coercion as a quick, desperate expedient, the program developed "interrogation plans" to disorient, abuse, dehumanize, and torment individuals over time. The plan employed the combined, cumulative use of many techniques of medically-monitored physical coercion. Before getting to water-boarding, the captive had already been stripped naked, shackled to ceiling chains keeping him standing so he cannot fall asleep for extended periods, hosed periodically with cold water, slapped around, jammed into boxes, etc. etc. Sleep deprivation is most important.