for some strange reason on house wiring it normally the neutral that causes problems but not all the time.
that burnt end is not due to water it is simply high resistance be it from corrosion or a loose connection. i think what might help cause this is how tight the socket is. if its real tight you have to wiggle the plug loose, and i mean the rubber part being too tight. when doing the wiggling you stress the contacts and open them up, next thing you know is its a loose connection