Unexplainable puddle the in boot

Hi guys. I noticed a week or so ago that I had a puddle in my spare wheel well (not like loads of water, but from the bumps inside the well area it collated puddles). See the 2 photos. I do apologise how awful the quality it is but I only noticed it late at night.

It’s not wet anywhere else in the boot, not even the spare wheel itself, literally just the fabrics lining underneath like in the photo.

In the UK it has been torrential rain and quite a fair amount of snow, but I noticed this before the weather turned. So I’m not entirely sure of the cause or where the water came from but I can definitely say it tried to dry up before the bad weather came in 5 days ago and now it’s soaked again like in the photos.

Any suggestions or recommendations of what it could be/how to resolve this. Like I said it’s not causing problems but I’m quite concerned if I leave it and it’s not drying up fully it’ll turn mouldy 🥲