An aqueduct is a channel or bridge built to carry water from one place to another, often across long distances. The word combines the Latin words for water (aqua) and to lead (ducere), so an aqueduct literally leads water where people need it.

The ancient Romans were masters at building aqueducts. They constructed massive stone bridges with multiple levels of arches to carry fresh water from mountain springs into their cities, sometimes spanning dozens of miles. These aqueducts used gravity to keep water flowing downhill at just the right angle: too steep and the water would flow too fast and damage the channel, too flat and it wouldn't flow at all.

Modern aqueducts work on the same basic principle but might use pipes, tunnels, or concrete channels instead of stone arches. California has an enormous aqueduct system that carries water hundreds of miles from northern mountains to cities and farms in the drier south.

When you turn on a faucet in a big city, that water has probably traveled through an aqueduct system to reach you, just as it did for people in ancient Rome.