An aqueduct is an artificial (man-made) channel that is constructed to convey water (properly called a canal) from one location to another. Many aqueducts are raised above the landscape, resembling bridges rather than rivers. Sufficiently large aqueducts may also be usable by ships. They are a kind of viaduct, carrying water instead of a road etc. While a road bridge often carries the road at a more elevated level than the rest of the road, such a variation of height is not possible for an aqueduct, of course.

Aqua Claudia, Rome

Historically, many agricultural societies have constructed aqueducts to irrigate crops. Archimedes invented the water screw to raise water for use in irrigation of croplands.

Another widespread use for aqueducts is to supply large cities with clean drinking water. Some of the famed Roman aqueducts still supply water to Rome today. In California, USA, a large aqueduct runs in the central valley that transports water from North California to the Los Angeles area.

In modern civil engineering projects, detailed study and analysis of open channel flow is commonly required to support flood control, irrigation systems, and large water suppy systems when an aqueduct rather than a pipeline is the preferred solution.

Navigable aqueducts include:

• aqueduct near Roelofarendsveen, Netherlands: carries the Ringvaart canal over the A4 highway and the HSL being constructed, which are situated on land below the level of the canal (and below sea level)
• Gouwe aqueduct, near Gouda, Netherlands: carries the Gouwe river over the A12 highway, which is on land below the level of the river
• the Pontcysyllte Aqueduct carries the Llangollen Canal over the River Dee in north Wales, and was designed by Thomas Telford and opened in 1805.

Segovia, Spain

Roman aqueducts include:

• The Pont du Gard in southern France
• Caesarea, Israel
• Segovia, Spain
• Mérida, Spain
• Tarragona, Spain

See also irrigation, leat.