aqueduct - a conduit that resembles a bridge but carries water over a valley

duct - an enclosed conduit for a fluid

flue - a conduit to carry off smoke

millrace, millrun - a channel for the water current that turns a millwheel

passage - a way through or along which someone or something may pass

sluice, sluiceway, penstock - conduit that carries a rapid flow of water controlled by a sluicegate

spillway, wasteweir, spill - a channel that carries excess water over or around a dam or other obstruction

tube, tubing - conduit consisting of a long hollow object (usually cylindrical) used to hold and conduct objects or liquids or gases

waterspout - a channel through which water is discharged (especially one used for drainage from the gutters of a roof)