An act of torture committed outside the United States by a U.S. national or a non-national now within the U.S. is punishable under 18 U.S.C. § 2340. The definition of torture used is as follows:
"torture" means an act committed by a person acting under the color of law specifically intended to inflict severe physical or mental pain or suffering (other than pain or suffering incidental to lawful sanctions) upon another person within his custody or physical control; "severe mental pain or suffering" means the prolonged mental harm caused by or resulting from - (A) the intentional infliction or threatened infliction of severe physical pain or suffering; (B) the administration or application, or threatened administration or application, of mind-altering substances or other procedures calculated to disrupt profoundly the senses or the personality; (C) the threat of imminent death; or (D) the threat that another person will imminently be subjected to death, severe physical pain or suffering, or the administration or application of mind-altering substances or other procedures calculated to disrupt profoundly the senses or personality;
Waterboarding CERTAINLY meets this definition. It is beyond dispute.
The only folks who dispute it are those who have done it, ordered it, and fear prosecution for it.
That's not to say that it should not be done. I would HAPPILY waterboard a known terrorist to discover his supporters and collaborators.
Your opinion is beyond dispute to Dems and John McCain. Even McCain tacitly admitted it didn't meet the definition when he insisted on new legislation that in effect made the Army regulation on treatment of prisoners federal law. The Army reg did not just prohibit torture, but requires humane treatment and prohibits physical harassment. The Army reg has been applied to all uniformed services. That is why it was legal for CIA to waterboard but not legal for the uniformed services.