Water in the Number 1 Cylinder
 

I have a 2001 F 350 with the 5.4 V8 (Gas). I brought it to my mechanic because it was running very rough. I don't drive it regularly. He found water in the number one cylinder. Cleaned it out and cleaned up the plug. It ran fine all the way home. It sat for 3 weeks. I went to start it up and the same thing happened. I ran it a while and it cleared up. Anyone ever have this problem before and if so is there a fix for it?