The Archimedes' screw is a simple machine used primarily to transfer water from a lower-lying body of water into irrigation ditches. It consists of a screw inside a hollow pipe. The lower end of the device is put in the water, and the screw is then turned (usually by a windmill or by animal or human labor). As the bottom end of the tube turns, it scoops up an amount of water. This puddle of water will slide up in the spiral tube as the shaft is turned, until finally it falls out from the top of the spiral tube and feeds the irrigation system.