Leakage passenger side LHD in carwash

[Hanzs]

Hi,
Whilst my T6 Multivan was going through the carwash a lot of water entered the interior on the passenger side (left hand drive).
It was a quite large flow which only lasted a few seconds.

Can anyone indicate what my cause this? I read so topics regarding blocked drains, but I'm not sure what to do now.
Thanks for your comments!

 

[dubber36]

Hi,
Whilst my T6 Multivan was going through the carwash...

I can't get past that part of your post.