Slipmatwax

I live in rainy Vancouver and have recently noticed water in the rear passenger foot well of my 2000 S4 B5. I vacuumed it up and kept my eye on where it could be coming from and even mentioned it to my mechanic. I didn't drive it through Christmas and New Years and looked today at the foot well. It was at least 3" deep with water and was deep enough it flowed into the drivers foot well.

It has been pouring with rain here for two days straight so I was guessing it must be coming in from the sun-roof and somehow draining down the door pillar to the rear passenger floor, but the sun-roof mechanism was dry when I opened it. Any ideas anyone? A trip to my mechanic to search for this will likely be expensive (labour) a few go-to tips will help a lot.

It is still not out of realm of possibility that is coming from the standing road water as I drive, but for this much water to have accumulated I think I would have noticed it sooner (I didn't check it after I got home).

K04-S4

Check the two water drains under the front hood cowl. One is underneath the battery and one is underneath the brake booster unit. Pull the battery to clean that one. If these are plugged then the tray can fill up will many gallons of water and spill into the passenger side of the interior via the Cabin Air Filter vent and potentially other openings too.

S4zAudihere

You could also make sure the drains for the sunroof are clean, get a blower nossle for a compressor and follow the tracks to a drain hole and blow it out. But most likely it's crap built up where ko4 said. I had same problem on passenger side after I installed my stereo and didnt put the rain collars back properly. it's under the cabin air filter on the passenger side. I can take a pic if your still stumped