It's not a means of information extraction.
I will admit there are methods of information extraction that are more reliable than waterboarding. However, many of them require one thing usually in short supply: time.
Here's a thought experiment for you to consider:
Think of the person (or people) most dear to you in your life. They are kidnapped. You managed to capture the kidnapper yourself only to find out that those dearest to you will die in a matter of hours unless you can extract their location and have them rescued. The kidnapper is zealous, resolute, unyielding. None of the "more effective" means of information extraction are available in the short time you have before your loved ones are killed. Do you (a) do nothing, and let them die, or (b) use whatever means available to you -- including waterboarding -- to attempt information extraction?
I challenge anyone to realistically choose option (a). The partisans in this argument will blithely say they'd choose the moral high ground, but in reality they would not. If lives are at stake -- lives that mean something to you -- you do whatever you have to do to save them, morals be damned.