I had the same problem a few months ago. It is easy to get underneath the carpet. You have to remove rear seat and remove the bolt on each side to take out the panels holding the carpet.
I put some large object underneath the carpet and let a fan blow air directly underneath to completely dry out the carpet (especially the noise insulation foam that soaks up a lot of water). I got a suggestion from one of the forum member to put baking soda underneath the carpet after it is dry to remove any odor or avoid mildew.
One of members posted this http://www.bimmerfest.com/forums/sho...7&postcount=10
Still a newbie until I change my VCG, VANOS & Coolant system...
Repairs so far - Steering fluid pump ($1k - Indy), CCV replacement ($1k hosed to another Indy) & Axle replacement ($850 to another indy).. 3 indys to date and now I am diving all in as a DIY'er