Common problem on the A6 model. Check at the bottm of the windscreen,
and you will see that the windcreen is sealed with a moulded black plastic
This sometimes detaches from the windscreen allowing water to seep through.
This then travels down through the aircon filter and collects in the
on the passenger side.
It should be possible to "snap" this trim back on. It eventually came off
on mine, I am waiting for a replacement.