Sometimes water gets into the sparkplug valley. If it does the engine may not start or may run rough. Prevention is better than curing: water usually gets in through bad seals around the plug wires and/or valley cover gasket.
If you do have water, try one or more of the following:
- Mop up as much water as you can with cotton-balls twisted thin, or rags wrapped around a screwdriver. Once you have as much water out as you can, you might try removing the spark plug. Don't do this if there's any chance of water getting into the chamber.
- Use a wet-dry vac (a powerful vacuum cleaner), and a long skinny extension (or a piece of heater hose) and just try to vacuum the water out.
- Remove the center valley cover, and dry it out with towels or rags. Let it sit for a while to make sure the water is dried up.
Once you've got as much of the water out as you can, spray a little WD40 in the valley. This should help dispel the water.