a passage (a pipe or tunnel) through which water or electric wires can pass; "the computers were connected through a system of conduits"

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
sluice / sluiceway / penstock - conduit that carries a rapid flow of water controlled by a sluicegate
spillway / spill / wasteweir - 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)

    passage