It is a simple fix. I'm assuming you are talking about the starboard side wiper. There is a nipple that is attached to plastic tubing that feeds fresh water onto the starboard side window washer. There is a knob at the helm that turns the washer on and off. If it is on and the plastic tubing inside the washer motor housing has fallen off or broken, water will drip into your cabin.
The windshield washer knob is on the starboard site of the helm station.....near the cup holder where your right arm is. Turn it all the way counter-clockwise to close it. If you go to your bow and look at your starboard side windshield wiper, you will see a tube that runs into a plastic fitting on the deck. The plastic fitting is held on by a single nut that is accessible when the wiper motor cover is removed from inside the cabin. The plastic fitting is prone to break, which may be what happened to yours. It is available from Grady. I had to replace the whole assembly earlier this year.