ok got the same problem, I have removed the carpet in mine removed the padding, and black front hump padding and dried them all out the carpet if in good shape should be cleaned out on your drive way with hose and detergent, mine came out great, now back to the problem of the water leak, dry the car out with sponge let dry and then when dry use a hose to simulate rain, in the cowl intake, you should see the results about 3 minutes after the water goes down the screen a small trickle slowly fills up the front of the floor pan on the passenger side also some goes over to driver side, this is the air intake the part which allows air to come into the car from the outside, to fix this remove the wipers completely and remove the cowl screen buy removing the plugs holding it down use a vacuum cleaner to remove leaves and debris pieces from the trough, now to the plenum it has gasket seals which have become leaky two things you can do disassemble the unit and use gasket sealer (drip check, silicone cement) and reseal, let dry and test, this should do it Emil Haverick

Don't forget that beyond this the cars will also develop leaks from the seams themselves where the seam sealer has become old and cracked. Filling that in will help fix all other leaks.

I also noticed no one mentioned possible heater core leaking. Water is one thing but are you for sure its not radiator fluid. When the heater core goes out a lot of the time they crack and cause a large puddle on the passenger side of the car. Why the passenger side I'm not sure but it is actually a comon problem with Chevy in general. Might want to check it it's fairly simple to remove everything you need to see to be able to check it just be careful it's all plastic and easly broken.

Our cars have a heater core box drain, so that should never be an issue unless your box is cracked. They will dump the coolant right to the pavement.

Also with heater core blowing out you have more issues than a wet carpet.

Very true I've actually had the core crack in a car on us one day the smoke that pours out from al your vents and whatnot is no fun at all