So I was surfing the internets and somehow came across water intoxication.
It's where when you drink too much water, your cells begin to swell, and you will most likely die from the result in your head - your brain swells and pushes against your skull, producing an effect much like if you squeezed on a balloon, only the balloon is filled with brains. As you can imagine, the sensation of having your brains squish against your skull (you will feel this before you die) must be rather unpleasant.
I was thinking - what if when you needed information from someone, (you had to interrogate them) you forced them to drink however much water ( you'd probably have to waterboard them or something to get it down), and then put salt on a table in front of them (they're chained or otherwise can't access it) and informed them that they would die unless they got the salt. I think being informed of how you're going to feel what is basically like an all-brain concussion unless you got the salt. The onset of symptoms - the massive headache, loss of sensory function and whatnot, would seriously add to the panic.
What do you think? Good idea?
Also, think of your own interrogation techniques (make some up!), i wanna hear them for my own sadistic pleasure :3