Water will seep through wherever it comes in (sunroof, doors, broken drains, etc.) after it rains, snows, or any other moisture you can think of, like car washes. Water will dampen the front passenger side floor and completly flood the backseat with about 3 inches of water. Headliner also gets wet and actually started to mold, so I removed it (it was an ugly sagging mess of moldy fabric, yuck). The water goes through and will eventually cause rust in the floor, but I use a dyson vacuum to get the water out, and that worked pretty well. In Florida, however, visiting friends, the humidity got to the car and made the windows fog up with condensation, thus creating a lovely wet car to drive around. Back in North Dakota the snow sat on my car for days, then of course the melt flowed into the backseat and sat there for a week. I didn't drive the car either, and the below feezing temperatures started to make a mini ice rink back there. That made some problems for me, and I eventually got rid of the water as best I could. I think that the car was on it's last legs when it slid into a tree, I'll never quite know, but my other Bonneville (yes, I had two, now one) has the same problem. I'm moving in Febuary to a milder state in the south, so hopefully the humid conditons won't kill this one too!