I had the same problem with my a4 b5 the water eventually built up so much that it made its way into the footwell. There is a drainage hole under the battery after I cleared the hole out by ramming a screwdriver down it the problem was solved. I used this YouTube video to help me. Hope This helps A bit :)
No Problem! :D
I believe there is one there and also another one on the other side (drivers side), your battery is passenger side isn't it? :s
Keep us updated John
Kind Regards
Bradley