Start by seeing if the water is coming from the bottom of the door (quite common). You can remove the door panel and re-seal the vapor barrier.

 

https://youtu.be/gaGQd6WweEo
This video is exactly what is happening.

There is a lot of water under the carpet, in a cavity visible by removing the plastic drain shaft under the driver seat.

I guess the purpose of that drain is to collect water from the passenger feet. How can it be clogged?

 

That is not a drain, it is for the clips for the floor mats. You place the plastic clips in the holes in the carpet and the floor mat secures onto the clip.

You most likely have a deteriorated vapor barrier in the door. Remove door panel and you will see it. Seal the bottom back and your done. I have had the same thing happen and that is what it is. The carpet has foam and cushion under it acting like a sponge to the water. So when you repair the barrier you might have to remove the carpet to dry it

 

Yes, but there is a black plastic shaft there which connects to a cavity under the passenger feet area. That cavity is full.of water.

 

There is a space between the carpet and the undercarriage that should be dry. You are just pressing water up through the mat velcro fasteners as the previous person said.

The first 2 places I would look for water ingress:

The doors have a vapour barrier membrane that could have come unstuck. This happened to my wife's F45 and the Butyl tape fixing the membrane to the door may just need heating up and re-affixing. To check, remove the door panel and get someone to spray water on that door (outside with the door closed of course) while you sit in the car. It will be obvious if water is coming in at that point.

The second is that water has been known to come in via the drains inside the engine compartment. These get blocked up around the Aircon blower which is at the rear of the engine bay on the passenger side and the water pools and then slowly trickles into the car. As you drive the forward motion pushes that water to the rear footwell see this post which has a video showing where the water comes in:

http://forum.bmw5.co.uk/topic/116098-heavy-rain-water-leak/?do=findComment&comment=1277207

 

Check the vapor barrier seals on all four doors, sunroof drains (all four corners) and the AC evaporator drains. You will probably find the problem working that list in that order. Stop the water from coming in and you should be good to go.

 

The car doesn't have a sunroof and I seriously doubt the vapour seal on the off-side of the car would allow water to pass over the transmission tunnel to the rear foot well on the near-side.

A leak from behind the glove box (on right hand drive cars) has been previously documented on these forums. This could of course be related to the Evaporator drain but again with that much water I doubt it. That is almost certainly rain water (or car washing water) ingress.

 

Probably vapor barrier, this is a known issue dating back at least to my 99 528. Amazing that Fine German Engineering can't fix a simple problem. I have had two CPO's that had ding repairs done. My theory is that this can cause the issue by the forcing of tools down into the door if they had to go that route. If you have had any ding repairs on that rear door I would be you $100 it will be the vapor barrier. A body shop can replace it for you a lot cheaper than the dealer.

 

Complained about this to dealer (in for an oil change). NOT COVERED. They want $239 just to diagnose the problem. Problem is simple - they don't know how to seal a door. The fact that you can find at least 30 videos on YouTube showing various ways to repair this at home on various models of BMWs makes that pretty clear. That and the hundreds and hundreds of posts on the various forums back it up as well. Not one single car I have owned has ever had this problem.
Watch the video a few times and do it yourself. Only alternative is to pay the dealer $$$. If not comfortable, find a good indy shop who will do it cheaper.

 

Yeah this is very ridiculous. I've had the same thing happen on all three 5 series I've owned. It is absolutely pathetic that a company that Prides itself so much on driving Dynamics and cutting-edge Technology, can't get something as simple as a damn water barrier right. What's the use of having a nice car if it's going to be flooded all the time?

 

Decided to write BMW NA about why they don't cover bad door seals on their CPO'd cars. Here is their response:

"Dear Dr. Frysztak:

Thank you for your reply.

It is at the discretion of BMW NA to offer specific parts coverage under the CPO warranty. We are unable to share a reason or justification for why we choose not to cover a certain part.

If you have additional questions that we are able to answer, please reply to this e-mail, otherwise, we suggest continuing to work with your preferred authorized BMW center to address the technical concerns with your vehicle."

This was followed by the ad: "BUILD YOUR OWN ULTIMATE DRIVING MACHINE.
Design the BMW of your dreams at www.bmwusa.com." :rofl:

 

So, in other words "Screw you! You stupid peons buy our luxury products and we leave you hanging dry to fend for yourselves, even on things where we should be ashamed of ourselves for letting happened for 20 years." :tsk:

 

I believe I found the problem: A water cavity under the hood, near the driver wiper (lhd) was clogged with leaves and water was not draining.

 

How did you come to narrow it down to this area? Can you post pics of the area in question?

 

^ That Ford dealer and Milli Vanilli appear to share a common philosophy of culpability.

 

I now poured a bucket of water on the windshield and the water drained very quickly.

But there is something else that concerns me now: I noticed outside wind is coming from the ventilation shafts under the steering wheel (somewhere at the knees), which didn't happen last year.

 

I now poured a bucket of water on the windshield and the water drained very quickly.

But there is something else that concerns me now: I noticed outside wind is coming from the ventilation shafts under the steering wheel (somewhere at the knees), which didn't happen last year.

Have you tried redirecting the Climate Control air to just the upper vents to see if that stops the noise you refer to?

 

Somewhere around that area, you have to stick your hand up to the elbow toward the center.

About the wind coming in, it happens with ventilation off also - there is air from outside blowing in.

 

Well this guy knows the culprit to this water retaining issue. Apparently it's a yellow color sealant grommet in the passenger side of the car. Replace it as he does and then you're good to go.

https://www.youtube.com/watch?v=PkZ-ZKGK5JY

There is also another way of doing it by removing the carpets but it's a hectic process. There be any DIYers this is a good challenge for y'all. See that video below.

https://www.youtube.com/watch?v=3lcC8dRC1sc