We like moist but not moist carpets

[aeo3]

Hi, just wondering if anyone can help me before I start jet washing my door seals to see if they're leaking.

My rear nearside passenger footwell is soaking, it's only just started recently.

Just wondering if there is any common faults that could cause this? It's in the rear passenger footwell and slightly under passenger seat and seems to have started getting wet in the passenger footwell too, and I know that ECU is there but it's ok so far.

I've checked the drains under the battery and it is fine, the bung had already been removed and was completely clear.

Is there any other common faults that could be causing this? I've checked the door seals and they do seem fine and look just like the other side, can't see any rips or tares < is that how it's spelt? Ha.

It's an 02 plate b5.5 estate

Thanks in advance for any advice !

Andy