I have an electronics board from an old vcr that I would like to use for an art project. I'm afraid of the capacitors, so is there a way to discharge them all at the same time? What if I submerged the board in water?
I can't think of a sensible way to do what you're suggesting. But if you want to discharge a big cap, just attach a resistor across it for a bit. Leaving the power off for a while will usually do it to.
If you're still worried, just probe a few with a multimeter.
Capacitors can't charge themselves and any charge they hold will leak away eventually even when nothing else is connected to them. When connected to a circuit board there are usually many paths for the charges to disappear down.
If it hasn't been switched on for more than a few hours it should be completely safe. Even the high voltage caps present in SMPSUs (if its a recent machine) have discharge resistors across them so they empty in a few minutes.