Waterboarding is not torture, according to that John Yoo memo.
https://en.wikipedia.org/wiki/Torture_Memos
The memorandum concludes with a narrow definition of torture, that its "severe pain" must necessarily be pain associated with "death, organ failure, or serious impairment of body functions". It also states that the statute requires "prolonged mental harm" to accompany mental or physical pain, and that "prolonged" means a duration of months or years.