The usual culprits on any car are the drains down the door shuts. If you open the door, and look at the bottom facing forwards, you'll see in the gap in the wing. Water from the scuttle panel runs down and drains out of there.
The other thing I've learnt from my car is that if you have an Activ, Sport+, 160SR or any of the other K12s with the added side skirts that they can trap a load of water and that pushes it in the other direction. At some point I need to take mine off and move a load of crap out of there.
When I cleared the drains on my K11, I basically just put a hose in the drain hole in the corner of the scuttle panel and blasted the crap out of the bottom, the water was blaaaaack.