Conduits are a type of infrastructure used to transport liquids, gases, and other materials. Aqueducts, ducts, mains, TUBES, and watermains are all types of conduits. Aqueducts are large-scale structures used to transport large amounts of water over long distances. Ducts are smaller-scale conduits used to transport air, gas, or liquid. Mains are conduits used to transport water, gas, or electricity. TUBES are cylindrical conduits used to transport liquids or gases. Watermains are large-scale conduits used to transport large amounts of water.