The Institut Français d’Archéologie Orientale (IFAO) has been studying since 1994 the site of Ayn Manawir. Human settlement is assessed on the site from the end of the Palaeolithic until the 3rd century AD. The Palaeolithic gatherers-hunters settled around artesian springs. By the end of the 3rd millennium BC, these springs dried up and men left the site. Starting during the 5th century BC (the first Persian occupation of Egypt), the digging of a network made of approximatively 20 Qanats, a technical innovation in that time in Egypt, allowed resettling. A mud-brick temple and houses in which dated documents were found, gardens and open fields scattered at the bottom of the slopes of the ‘Ayn-Manâwîr hill. The excavation and the detailed study of one of these Qanats and of the connected irrigation systems gave us the keys for understanding the tunnel digging method, the water resources management, and the history of the attempts to maintain the supply of water as late as possible. In addition, the datas given by the demotic contracts and by the floral remains allow us to rebuild the ancient environment. The existence of the huge underground water table under the Egyptian Western Desert, the peculiar geomorphology of this part of its oases allowed and made necessary the digging of Qanats to secure human permanence in this arid region.