are you located in the states?
if so there is a recall that should take care of your issue, if you provide your vin i can check to see if the recall is open.
you should check the drains under the battery.
remove the plastic cowl and remove the battery and battery tray.
there is a rubber grommit there you can remove.
oops i must of been confused, mixup of terminology.
is your car a sedan or a wagon?
you will also want to clean out the sunroof drains (front and rear)
the best way is to shoot compressed air through them to get the junk out, but sometimes you dont have access to that kind of stuff.
if you have a thin piece of bendable wire and you can stick down the drains enough to clean the junk out would also work.
a method you can use is by sitting inside the car and have someone hose the car down and while you on the inside check for water leaks.
VW Technician
VW Body Electrical Specialist, Expert Level Technician