Welcome to the Forums and beautiful Daytona grey colour choice! 😁
I’ve not heard of water in the sills, as unless you have a sunroof, the water can channel down there but there’s usually a drain port.
From pictures I see you don’t have this feature so I’m going to break some potentially bad news here.
Please see this link to see whether it’s similar symptoms...
I can hear what sounds like water sloshing around in a container to the rear of the drivers seat. It only occurs under sharp breaking/accelaeration (basically enough of direction change to cause the liquid to move). My car is due in for some warranty work soon so will ask Audi to double check...
www.audi-sport.net
So either faulty fuel tank or adblue tank empty... hopefully the latter!
~Alex
THIS IS WHAT I HAVE FOUND ON AN OTHER FORUM