Lots of water inside my car!! Help!

[Fondatron3000]

Today I took the car for a.drive and realized that the back seat was wet, upon further investigation i realized the entire floor of my car is soaked and that there was 2-3 inches of water in the spare tire compartment in the hatch area. I think the hatch/tailgate seal is the culprit but could it be something else??? (1992 Honda civic DX hatchback)

 

[Fondatron3000]

Also when I got the car back in 2016 I noticed that the board in the back was all warped and that there was water stains on the carpet on top of the board but thought it was something else, if this has happened repeatedly what other problems should I check for? the car runs great, doesn't have any electrical issues, it also has a little rust but not that much and when I had it on the lift it wasn't rusty on the frame, floor pans or anything