soak into the door panel. if you're getting a pool of water in the foot well, check to see if the bottom of the door is damp or has evidence of water staining. if it does, whip the door panel off and check the condition of the membrane. use waterproof tape to repair any tears, or replace the membrane entirely with plastic sheet.
the rubber seal around the edge of the door can also sometimes be a cause of leaks. if the seal gets damaged, or dries out, water will track down the front of the door and into the car. a visual inspection is usually sufficient to diagnose whether this 