Rain water in rear foot well

When it rains (as it does here in Oregon rather frequently) a small lake develops in the right rear foot well of my 2003 525i. The water is constrained to the rear floor, the door panels are not wet and I can find no avenue for this water to enter the cabin.

Can anyone tell me where this may be coming from?

Thanks!

Originally Posted by barabas9

Can anyone tell me where this may be coming from?

It's one of the top ten well known issues of the E39 (and other models).

Go to the bestlinks and type /vapor barrier F3.

Among others, you'll see this:
- How the vapor barrier works (1) & the problem with front & rear door vapor barrier adhesives which allow rain water to wet the carpet (1) (2) (3) (4) (5) (6) (7) & what adhesives to buy (1) & what sizes for the adhesive beads (1)

LOL newbies enjoying all the fine intricacies of the E39.

Case with my car, under side of door there is a hole that (originally) has to be plugged with a plastic cap. Check with other non leaking door for comparison.
Mine doesn't have that cap at leaking door. The leak went away after I plugged it with genuine cap.

It happens to all of us...as a matter of fact I just made the repair to the rear passenger side door on Sunday.....after repairing the drivers side doors last year....eventually you will have to do all of them....I have found that the best preventative measure in addition to replacing the butyl tape adhering the vapor barrier to the door is to apply aluminum faced waterproofing tape at the lower perimeter of the door to surely prevent them from separating again. I bought the tape at Lowes.