Thought I'd share this in case anyone else has this: My A3 has suffered
this *every year*
when the weather gets worse and the roads dirty.
Symptom 1: Spare wheel well full of water
Sympton 2: Right-hand side compartment (behind the boot side trim) also
full of water.
The solution is really simple- up behind the rear bumper on the right
hand side there's a drain bung: it's the type that's supposed to allow
water to drip out but not let any back in. Don't ask me why but this
keeps getting blocked with road dirt. If you flex it a bit the water
runs out, but the best thing to do is pull it out and wash it. There was
a good couple of pints of water in total- it overspills the side
compartment and fills the spare wheel well. You can't see anything amiss
until you lift the boot carpet and wonder why the spare wheel has
condensation on it.......