"It has been proven that no firearm can penetrate 14 inches of water, not even the magnum .50 cal sniper rifle with steel-jacketed bullets" - Alejandro

That's awesome. It's good to keep in mind though that the slower weapons, like muskets and older revolvers, will penetrate more (up to several feet) than the high-powered, high-velocity bullets. Water is a beast. It will not fight you as much if you're slower, but if you're fast, it will act like a nasty super-viscous wall. And if you're really fast, it'll turn into impenetrable concrete. Such an interesting substance. - Raoul Pop