It is torture. There just isn't anyway around it. The purpose of waterboarding is to give an individual the sensation that they are about to drown so that they will be in fear for their life and be willing to talk. That is torture, it doesn't matter how it is gussied up.
On the other hand, it does not cause permanant injury. When we find ourselves facing an implaccable enemy that does not recognize any nation and operates across international lines, and has proven itself to be resourceful and elusive, it may be the best option we can use to balance between the unacceptable extremes of becoming barbarians ourselves or missing necessary information because wew were too nice to use any method to get it.