Ok, so all was well, on my 2000 A6 until one day I noticed a large amount of water in the rear passenger-side foot area of the car. I followed the water's trail, and determined it was coming from under the dash through this spongy thing. It only leaks when the A/c is on. Could anyone please help me out here? My A/C is useless since it will damage the interior, and I live in Texas these 100 degree days are killer.

 

I have a 2005 A6 Avant. Same problem, water in passenger f/r footwell. Told that drain pipe on underside of vehicle was blocked. You should find this once black material cover is removed by undoing two 10mm nuts. Pull back cover from bodywork and you should find a rubber bung. Take this out give it a clean and cut a small v shape on bottom side of flap. This I have been told will cure the problem. I have done this today and have my fingers crossed. PS also drying out carpets now. Best of look. JC 66

 

Thanks for the reply. Let me know if this works out for you.