If it's in the rear floor board as well, it's not the windshield, unless you were driving around and the water sloshed back there.

You may want to chek the seal for the door, and the side window, that seems a lot more likely than the windshield.

This is gonna sound kinda stupid, but take off your panel that covers you "A" pillar, and but hose it off, and due it one part at a time, and see if you can see it leaking. If that doesn't work, take off your door pannel, and redo that whole thing, and see if you see a leak again. Also, consider that it may be an A/C leak coming from under the dash, and is just making it's way to the back due to driving around.

Let us know....
Aj