Boot letting water in?

Hey guys, I went in my boot earlier to get some boxes I left in the car last night... I came to find the bottom of them are a soggy mess, I lifted up my carpet and there's a pool of water! (from the rain last night)

I have no idea what is letting the water in, I think it may be the rear brake light.

I was just wondering if anyone has had a similiar issue, or anyone knows how to fix it!

Thanks!

Yeah rear washer jet works fine! There's no water marks from the roof (not entirely sure where aerial base is) but theres's a little grill just under the boot lid on the inside of the boot, which 4 or 5 lines in which seems to be the culprit, it's soaking...