The Aqueduct is a premium decoration from the Iron Age. It doesn't require a tech to be researched, all the player has to do is reach the Iron Age. Its happiness output can be doubled by polishing it.
+51.67 per tile.
Your decoration can be polished to double the happiness provided to +310 for 12 hours.
In update 1.85, the graphic of the Aqueduct was reworked. The water flowing through the Aqueduct was removed.