Typically, if governments want more water, they invariably demand a new dam. But there are other ways - ways that are often more efficient, cheaper and give control of water supplies back to the communities who use them. Some believe it is time for a revival of ancient techniques in a modern setting - techniques that were forgotten during the 20th century could make a comeback in the 21st. Take the long underground water tunnels known as qanats. They are one of the great engineering treasures of the Middle East, Central Asia and North Africa. In these arid regions, rain falls only sporadically and mostly in the mountains. The water swiftly percolates underground. The Persians long ago learned to excavate these springs, 'chasing' the water back into the hillside by digging horizontal tunnels.
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