1994 Mercury Grand Marquis wet floor.

My 94 Mercury had a lot of water on the passengers side rear floor and also under the driver's seat. The carpet was dry on the sides and also on the firewall area. I am really puzzled. It happened to collect while the car was sitting and we had rain for a day or so. I have a Volvo do that on the passengers side front floor, but that was a plugged drain under the wiper cowling and it would seep down the fire wall. That made sense but this does not. The passenger side front is dry. Any ideas where this water might be coming from? I checked the pass. door moldings and they look fine. The trunk is also dry. Any help would be appreciated.

I did some research and found these two youtube links:
I will be trying the under cowling fix first.
https://www.youtube.com/watch?v=tYHikiM1e88
https://www.youtube.com/watch?v=2XEzvKbXzG8