You don't have to grab a bottle of something and force it down someone's throat to be culpable if they die because of it. If you set the situation up, encourage them to do it despite knowing the risks, tell them things about it that are misleading, and blow off people who warn you about the danger you are putting these people in, you don't have a leg to stand on either morally or legally. These radio station people are going to find out a lot about personal responsibility in the coming months -- and they'll find that theirs is a hard thing to duck.
OK. Suppose you buy a ticket to a show where a motorcyclist is going to jump 16 buses. When he gets to the top of the ramp, he looks like he's going to chicken out, so you stand up and chant "you can do it, do it, do it". Your neighbor is yelling "don't do it, it's not worth it", and you and those around them chant louder to drown out their warnings.
He drives back, takes off, lands on the 16th bus and dies.
Are you liable? You PAID him to do something so dangerous that you knew he could die, and then you encouraged him to go on with it, yelled that they could accomplish the task when they couldn't, and dismissed and blocked those who were trying to warn him not to go.
BTW, I think the reason they joked about dying was because they were convinced you couldn't die from drinking a little water. They knew about the college kid, but said they didn't believe the story, that there was probably drugs involved but it was being white-washed.
Their joking was entirely consistant with people who had HEARD something, but didn't believe it, and wanted to make fun of it. I don't think they believed it was possible for a person to VOLUNTARILY INGEST enough water to kill them. They thought if it was dangerous, the contestants would throw up, and they had warned the contestants of that.
However, I have come to the conclusion that they were negligent, if only because they knew enough to at least get a professional opinion, and it sounds like their advice, while being believed by them (making them not deliberately negligent) could easily have been construed as having been INFORMED ADVICE, when in fact they hadn't been informed at all.