Passenger side carpet wet. What is the best way to find the leak. I tried hosing it but didn't see water coming in anywhere.

When I hosed the car down, it looked like there was a place at the top of the windshield where water was running in. However, it wasn't running inside the truck as far as I could see. Pulling the carpet back, I couldn't see any water running in anywhere. I did notice the foam sound pad on the inside of the fire wall was soaked but I couldn't see any streams of water there either. My only other guess was maybe it got wet when the a/c was on. But even if that is it, it looks like a major undertaking to find and fix. I will appreciate suggestions.