My house’s basement has a small kitchen area with a sink. I can’t figure out how to turn the water on to the sink. When I turn the valve on the left, I can run the sink but the third water line (which isn’t connected to anything) will run while I use the sink. When I turn on the valve on the right, the third water line runs no matter if I’m using the sink or not. Should I just cap this? Is this a refrigerator line?