I've had this problem a few times. Open the glove compartment and also fully open the control on the heater controls to circulate the air. If you look inside, you can see the air filter spinning (if engine running) around inside (don't put your fingers in). Just above it, you should see lots of puddled water. That will confirm the water is coming down the air vent. If you remove the scuttle panel and look inside, you can see the opening for the air vent. Somehow the water gets down that vent. Just try to clean and dry all around where the water might be entering and seal it. Use a hair dryer to dry it before sealing helps a lot.