I had that happen to me in an old VW Golf years ago. The problem with the water collecting down on the floor is that it got very stagnant in the summer months, and oh yeah, when it was real hot, my car steamed up from the inside like a sauna. I'd have to start it and wait 10 minutes with the front and rear defrost on full blast while the condensation cleared. My car smelled like a locker room full of dirty gym socks after a short time of having standing water on the carpet. I searched and searched for how the water was getting in but never could find it.

My solution was very easy, effective and crude. I got under the car with a drill with a small bit and put 2 small holes in the footwell (not the carpet) to drain the water. Problem solved...