First off, the main thing to be taken away here is that just because you CAN do something doesn't mean it's a good idea.
Any AEG can survive being submerged. Take it out of the water, give it a good shake to get some of the water out of it, and you're good to go. DC power conducts very poorly in water, so the chance of a short circuit or burning something out it next to nil. I wouldn't try that with a PTW though. They're very sensitive to moisture due to their circuit boards.
That being said, I would recommend that anyone that gets their gun very wet give it a good cleaning afterwards. Any steel parts will start to rust. The last thing you'd want is rusty mechbox internals. That could definitely cause some problems.