A few weeks ago after a heavy rain the rear carpet in my car was under about an inch of water
I dried the carpet with towels and a fan and watched youtube channels to find the problem and solution
I don't have a sun roof so I didn't have to worry about tubes from the roof.
At first I checked my inner door cards which were not sealing so I resealed them and hoped I had fixed the problem
Two nights ago there was another big rain and the same result except now my front carpet was wet too
I pulled out the drivers seat (RHD) and the carpet
The entire floor was under water with all the electrical and foamed soaked
I found the water was coming in through the bonnet release rubber that was not in the hole properly
I refitted the rubber and then removed all the trim from under the bonnet and half the brake booster was under water
The water drain was completely blocked with leaves and mud
So no water was escaping
The water level would rise and then flood through the bonnet cable rubber into the car and fill the floor under the carpet with water
It had been leaking for a while as there was rust under the speaker which I had to fix also
Tonight it is raining again so I will test to see if I have fixed the problem after repairing everything drying everything and putting it back together

 

Thank you for this and the pictures! Although I do not have any leaks from the front, I will check these out and clean them out just in case, keep us updated.

 

I have the same problem. I can't find that plug. where is it under the hood at

 

My car is a RHD but yours will be exactly the same but on the left if it is a LHD.
If you remove the plastic cover under the dash which covers the steering column you will be able to follow the bonnet cable to the rubber grommet that seals the hole it goes through.

Under the bonnet you have to remove the air box to get to the container that surrounds the power brake booster

You wIll easily see the rubber grommet for the cable and the water drain that is blocked

 

Just a quick update
It's been pouring here recently but I have no reoccurrence of the wet carpet.

It's perfectly dry!

I hope my success may help others if you have the same problem