Aqueduct and Water main

Aqueduct noun - An open man-made passageway for water.

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

Water main noun - Main (a pipe or conduit) for conveying water.

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