Have you got a sunroof? I'll take it that you dont until you answer and give you some dif advice. under the wiper panel (black piece of plastic arounds wipers) may be blocked with leaves etc, note i said UNDER. This is really hard to explain but open your bonnet and have a look around at the back of your engine bay, either side there'll be a area where water runs off the window, the water then runs from this down holes, the holes could be blocked. hope this helps, if you need it explained better please say.