overzealous detailers that usually happens when someone rinses a motor, and the plastic cover has a crack or a missing bolt cover. You can blow the water out with air pressure, or make a paper or cloth wick and cram it in, letting it air dry, but it should boil out when it reaches operating temperature. Or you can get an alcohol based brake cleaner, put the straw from the nozzle down in the plug hole, and blast away, any cleaner left over will evaporate more quickly than the water, but it is flammable, so be careful until it is dry. Of course, all these things are done with the spark plug in place.
