when a spark plug gets wet, throw it away

"It doesn’t necessarily have to be replaced; it depends how long it’s been wet. When a spark plug gets wet, an insulating layer is basically formed between the electrode and the core of the spark plug, stopping it from creating a spark. By removing the insulating layer and cleaning it properly or, better still, using an appropriate sandblaster with extra fine grit, you can regenerate the spark plug without damaging it and re-use it without further issues."