Cure your rainwater problems before you replace it or the new one will drown too
Open the bonnet and check the rain tray isn't cracked as said, if it is go to VW they sell a better designed one made out of thicker plastic that wont crack. Then take it out along with the small one on the left side and look in both corners of the scuttle area, make sure the drain holes are clear of leaves/dead mice etc otherwise water will back up and leak in everywhere.
Check for missing/loose grommets, on the passenger side whack a ton of grease round the base of the fresh air intake grill, or remove & replace the seal. On the driver side do the same for the bonnet release grommet, or you'll get water in ya fusebox.
Other causes of water leakeage are the sunroof drains being blocked, the drainpipes exit in the front & rear arches. Open the roof and pour a little water in to make sure it drains quickly. Next have all the door cards off and check the plastic seals behind the door cards, if there are any splits rip em off & replace with some decent plastic sheeting and tape down with waterproof duck tape. I always cut an extra sheet to half the hight and stick it to the bottom half of the door frame, and tuck it in at the bottom, this stops any water running down the seal and pooling at the bottom.
