I noticed when I bought the car (rather overpriced for all the problems it had, but it has low mileage and I HAD to have a car), after a heavy rain, there is a puddle of water in the passenger floorboard.

After searching, I see a lot of people saying it's the cabin air filter or something like that, but they say the leak is in the corner.

This water puddle (at least a cups worth depending on the rain) is in the dead center of the floorboard, and there is no trail of water on the carpet to show it's leaking from any direction.

There is no water on anything else I could see, and it just appears to magically pop into the middle of the floorboard. Ideas?