Hello, I've searched many threads on this forum and on search engines to find the cause and solution to my water leak problem but this one seems to be different from the common water leak in the passenger footwell and related ones.

Whenever it rains heavy it get soaking wet under the rear passenger seat (insulation pad). This makes the seat itself and where you rest your lower back wet too.

(Replace the underscore for a dot. Mods, edit and place the links for me, please.)
i.imgur_com/qujC63g.jpg
i.imgur_com/FcZ64cb.jpg

I've intensely searched for leaks around the rooftop, windows, doors, boot and nothing seems to be leaking.

Here's a quick video hopefully showing better where exactly is the most wet.
youtu_be/gK6PU5PceTY

I have no idea what the metal bolt thingy is about but my guess is the water is leaking onto the seat from there. I've tried to unscrew it but to no success. Maybe with a strong electric screwdriver.

Where could the water be coming from tho?

Sorry for the bad quality and thank you.

Your best bet is to take rear seats, carpets,all interior,plastics in boot area,then make sure everything is dried out and cleaned,then sit inside car with a torch while somebody is outside your car with a power washer,and watch for where the leak is while there soaking the car on the outside,
Its only way to find out for sure where your water leak is entering car

The shiny chrome thing in your video is a locator for the seat. There is another one on the other side of the car.

Is your seat getting wet after you drive in wet weather? There should be a large round plastic cover under the seat to access the petrol pump.

It seems though that water is somehow coming from above to get to that location rather than from below. Bit of a mystery!