waterline

noun

1. the line to which the surface of the water comes on the side of a ship or boat
2. any of several lines parallel to this, marked at various heights on the hull of a ship, indicating the various degrees of submergence when the ship is fully or partly loaded, or unloaded, and on an even keel
3. ☆ a pipe, tube, or other line connected to a source of water
4. watermark (sense )