[T-sport]

A similar thing happpened to my A3 as well and it turned out to be the pipe that clips on to the washer jet had come off and this in turn ended up with the boot lid filling with water after a period of time..

I just pulled on the plastic backing trim and unclipped as markiestartby says and all became clear straight away.. Just cut a few mm off the pipe and re attached alls good now !!