Water line and Water pipe

Water line noun - A line marking the level reached by a body of water.

Water pipe and water line are semantically related in waterway topic. In some cases you can use "Water pipe" instead a noun phrase "Water line", when it comes to topics like conduit, water main.

Water pipe noun - An oriental tobacco pipe with a long flexible tube connected to a container where the smoke is cooled by passing through water.

Water line and water pipe are semantically related in waterway topic. You can use "Water line" instead a noun phrase "Water pipe", if it concerns topics such as conduit, water main.