ancient type of water-supply system developed and still used in arid regions of the world. A qanāt taps underground mountain water sources trapped in and beneath the upper reaches of alluvial fans and channels the water downhill through a series of tunnels, often several kilometres long, to the places where it is needed for irrigation and domestic use. The development of qanāts probably began about 2,500 years ago in Iran, their technology then spreading eastward to Afghanistan and westward to Egypt. Currently, several thousand qanāts are still used in Iran and Afghanistan, chiefly for irrigation.