The answer to 'water line or water line' is that they are the same thing. A water line, also called a water pipe or service line, is the underground pipe that brings fresh water from the municipal water supply or a well into your home. It is the main source of water for your entire plumbing system.
Water lines are typically made of copper, galvanized steel, or plastic (PVC or polyethylene) and can vary in diameter from 3/4 inch to 1 inch or more depending on the size of your home and water usage. The water line runs from the street or well to your home's main shutoff valve, usually located near the front of the property.