The Great Man-Made River resides in Libya and is one of the late Muammar Gaddafi's pet projects. It is an enormous network of wells, pipes, reservoirs and other infrastructure that supplies groundwater from the Nubian Sandstone Aquifer System in SE Libya northward to the cities of Tripoli, Benghazi, Sirte and other metropolitan areas, and to various irrigation projects along the way. Some consider it the largest irrigation project in the world. According to their website, it's a network of pipes and aqueducts over 1,600 miles long being fed by more than 1,300 deep wells in 6 wellfields. This system is reported to withdraw and transport 1.921 million AF per year.
Efforts to find oil in southern Libya in the early 1950's led to the discovery of the groundwater being tapped. The project itself was originally proposed in the late 1960s - just before Gaddafi became the Ruler of Libya in 1969, but actual work didn't begin until 1984 with the construction of the first of five phases. The total cost of the project is projected at more than $25 billion.
The groundwater supplying this system is from the Nubian Sandstone Aquifer System which accumulated during the last ice age and is not currently being replenished. It is a hard sandstone aquifer covering parts of four African nations - Egypt, Libya, Chad and Sudan. It ranges in thickness from 400-700 feet thick, but can reach 1500 feet thick in areas. According to Wikipedia it contains fairly good quality water - from fresh to slightly brackish.
There is a bit of a disagreement on the longevity of the supply, however. The project claims supplies will last 1,000 years at the 2007 withdrawal rates, while independent analysts project a more modest 60-100 year lifespan. I wonder who is right? And perhaps more importantly, I wonder who Egypt, Chad and Sudan are more prone to believe?