if a VW, almost certain to be water coming in the ventilation system because the drainholes are blocked. These carry away water that runs off the windscreen, past the wipers and in behind the bonnet.
My Skoda filled up with a couple of gallons of water for this reason early in the summer when the rain was so heavy. Don't know where the drain holes are actually, but the water builds up and floods into the car through the pollen filter.
Was charged a fair amount in the garage to clear the drain holes so if you can do it DIY then all the better - have a look under the car in the region of the front wheelarch, close to the doorpost.