The question of consequences is, of course, very broad, and includes such things as damage to our international reputation. In WWII, German soldiers preferred to surrender to the Americans than to the Russians, because they thought the Americans were far less likely to torture them. So it is possible that waterboarding might work in the narrow sense of being the most likely way to get the information we want, but it still might not be justified from a utilitarian perspective, because of the damage it will do to the reputation of our country and its operatives.
But, perhaps most important, is the question of whether techniques like waterboarding work. One common response to this issue is to say that it may well work to get information out of an otherwise silent captive, but someone in that position is likely to produce, not actionable intelligence, but rather whatever BS the captive thinks the captors want to hear. Unless we have good reason to believe that a harsh technique like waterboarding will not only work, but will get better results than other available techniques of getting information, the issue can't even be set up as a consequentialist-anti-consequentialist problem. If it turns out that harsh techniques like waterboarding are likely to give us the results we want, then the issue of can be cast in terms of consequentialism. If, on the other hand, other techniques are more effective and can get better results, then it would just be an example of the "toughness fallacy" the fallacy of thinking that certain methods of dealing with wrongdoers are more likely to be effective because they are tougher. As an example, we may think that the death penalty is a better deterrent than life imprisonment because it is tougher, but the question has to be settled empirically as to whether the death penalty is a superior deterrent than life imprisonment.
Anyway, former Attorney General Michael Mukasey argues that a large part of the information we used to get bin Laden came from intelligence received through waterboarding, but Chris Smith argues that waterboarding actually prolonged bin Laden's life.