06 Envoy Water in spark plug chamber?

I have a 2006 Envoy. It has a Vortec 4200 engine. It developed a misfire in the number one cylinder. I took it to the mechanic about 2 months ago and he said the spark plug chamber was full of water and it was shorting out. He drained replaced the plugs put a heaping of dielectric grease and replaced it. It ran great for 2 months. The miss returned. I checked it out same code misfire cylinder 1. I pulled the coil and it was full of water.

My question is how does this happen? It does not smell like coolant. It smells like water thats been sitting. I cleaned it up and the truck runs perfect. Any help would be appreciated.

A bad cowel could cause rain water roll, and flood your spark plug boss.

1) Put a garden hose with a little water pressure in the middle of windshield.
2) Pop the hood and watch the water roll!

If using Dex-cool (orange) antifreeze, it wont smell sweet like the old green coolant.