I agree. It sounds like you may have blown a head gasket and started pushing gases into the radiator. That will also allow coolant into the cylinder.
If the engine will move by hand (even a little), it is not likely a stuck piston.
If it is water in a bore, you maybe able to determine which bore by openning the closed exhaust valves one at a time and seeing if the engine will turn completely over by hand. The water should push out into the exhaust manifold.