I wonder if all of the fearful conservative water-boarding enthusiasts would be so keen on it if they understood that if it is deemed to be an acceptable government investigative tool, there is no reason it cannot be used for domestic purposes. As, it appears, has already happened in Britain:
Metropolitan Police officers subjected suspects to waterboarding, according to allegations at the centre of a major anti-corruption inquiry, The Times has learnt. The torture claims are part of a wide-ranging investigation which also includes accusations that officers fabricated evidence and stole suspects’ property. It has already led to the abandonment of a drug trial and the suspension of several police officers.
If waterboarding is nothing more than an accepted means of official inquiry, then the British police officers’ logic is correct and there is no reason it shouldn’t be legitimately used in drug, tax, and other criminal investigations.