Fiesta 58 reg wter in boot

[gstev]

Hello all hope you can help, I have discovered that my sons fiesta has leak in boot, there was a about an inch of water in the spare wheel area. I have seen a small tear in the boot lid seal but cant see how it could result in so much water. The driver side carpet below the rear light is wet, passenger side appears to be dry. Has anyone had similar issue and got solution

Thanks in advance

Gavin S