In the water cure, the subject is forced to drink potentially fatal quantities of fluid and the resultant pain is increased by beating or stomping upon the distended abdomen and other parts of the anatomy. He will confess to anything. However ask him where his command post or safehouse is and you will get only gibberish in reply. He has no capacity left for rational thought.
On the other hand, the waterboard duplicates the panic of drowning by replicating the physical aspects. To avoid repeat performances the subject will start answering and/or correct previous falsehoods. Or to be more faceticious, hooking a field phone to the genitalia and turning the hand crank works, utilizing a 35 KW only results in fried terrorist.