A Good Cause

You and two other people are now left in the game. The first butler wheels out a dolly with a barrel of water on it. The second butler came in and handed everyone a tiny envelope with a card in it. Mr. Harley then explained that you could choose to open your card and do what the card says, or submerge you head in the barrel of water for two minutes. When you put your head in you are not allowed to come up for air until the two minutes are up. You were given first choice.

Do you open your card or do you dunk your head in the water?