Waterboarding isn't the only issue. Read this:
Why Sleep Deprivation Is Torture | Psychology Today
However, no matter who you quote, we've prosecuted both foreigners and American soldiers for waterwaterboardning in the past. However, if it's quoting folks you want:
. . . . McCain said he was “Very disappointed by statements at SC GOP debate supporting waterboarding. Waterboarding is torture.”
McCain: "Waterboarding is Torture" | Care2 Causes
But then again, he's merely a veteran who has been tortured. Surely not anything republicans would care about. Let's try someone else:
“It was well said—by Jean Tarrou in The Plague, I think—that attendance at lectures in an unknown language will help to hone one's awareness of the exceedingly slow passage of time. I once had the experience of being 'waterboarded' and can now dimly appreciate how much every second counts in the experience of the torture victim, forced to go on enduring what is unendurable.”
― Christopher Hitchens, Hitch-22: A Memoir
Quotes About Waterboarding (6 quotes)
There's just no doubt in my mind - under any set of rules - water boarding is torture. -- Tom Ridge
Torture Quotes Page 4 - BrainyQuote
And of course there are studies and the like that support me as well:
http://www.cgu.edu/pdffiles/sbos/costanzo_effects_of_interrogation.pdf
Is Waterboarding Torture? | waterboarding.org