If you have found water (lots of) in your rear footwell on the left
hand side of the car then read on. I recently followed the advice in
the following link and was amazed at how effective it is. Please bare
in mind if your carpets are wet then there will be a tidal wave
underneath so you must get them lifted, remember you have the CCM in
the front and the wiring loom from front to back (none of which mix
well with water). Lastly, this doesn't take into account for blocked
sunroof drains or leak doors. Check it out, Andy....

http://www.weirdlittlebiscuit.com/passat/leak/