Aqueduct

Aqueducts are structures capable of moving from a Noria to a Reservoir to provide irrigation.

Aqueducts can be built on top of Piers and Roads, but can't be built on top of Bridges or Drawbridges.

Aqueducts can also be built above Wells, Hovels and Farms, but not Orchards.

Aqueducts can be built through walls (before or after construction), but not gatehouses. (the wall doesn't carry the water, an Aqueduct pier built inside it does) If you want to, you can overlay your walls and aqueducts.