In the cemeteries of Graeco-Roman Alexandria in Egypt, archaeological investigations initiated more than a century ago attest to a usage of water for specific funerary purposes. From the foundation of the city in 332 B.C. to the third century A.C., fifty-one hydraulic installations can be entered in the accounts in Alexandria itself and its neighbourhoods ; most of the time water was made available inside the antique underground tombs, designed to accommodate the regular visits that the families paid to their dead. From a corpus that inventories the hydraulic structures identified to this day in the archaeological litterature, the different water management modalities are first described by their diversities. Wells frequently dug in the central court of the hypogea attained ground water and sometimes served as draining traps. Cisterns in the shape of little underground rooms equipped with a window or a vertical shaft, and sometimes with an adduction pipe, could store and conserve rainwater. Basins, as opened containers, directly offered water to the users. The reservoirs (basins or cisterns) which did not have any system of supply therefore depended on exterior installations, as all tombs that were totally devoid of hydraulic installations. The reasons that explain the presence of these water devices are various and suggest to consider the necropolis not only as a "dead city" but also as a life place. Water needs concerned the maintenance of locations, as well as the irrigation of gardens, whose rare archaeological remains are completed by Strabon's testimony (XVII, 1, 10) and by some juridical, epigraphical and papyrological documents that show the importance of kêpotaphia (literally the "union of a tomb and a garden") in Alexandria to the High Empire. The care of corpses required a lot of water as well, especially for the needs of mummification, whose adoption in the Roman period is confirmed by recent discoveries in the occidental Necropolis, where Strabon mentions "halting-places fitted up for the embalming of corpses". For the commemoration of the deceased again, the altars that frequently carried out into the tombs attest to sacrificial ceremonies, whose preliminary rites consist of purification ablutions and consecration aspersions on attendance and cult instruments. As a complement of sacrifices, some meals were eaten on site, according to banqueting halls discovered in the cemeteries under and above ground: in conformity with hygienic and traditional conviviality rules, water played a part in the washing of the hands, the drinking (some diluted wine), the swill of the floor and even the cooking in the equipping tombs. The imported and flourishing Greek culture often explain theses practices, in particular with the will to celebrate some deceased with heroic honours. But the progressive influence of Egypt and its specific religious customs has to be emphasized to determinate all the gestures about water and the origins of their beliefs. The special question related to the thirst in the hereafter in Alexandrian thought is very important from this point of view and induces a new orientation in the reflexion: from epitaphs expressing the wish for refreshing water after the death, in the Greek language but with the Egyptian god Osiris as the giver of the precious liquid, our analysis finally attemps to define the religious sources of the belief and the practical consequences in the tomb. Some hollow or pierced devices discovered in the funerary context remind of libations systems known in the Mediterranean Basin and tend to evaluate, from textual and iconographical documents, the role of water in the offerings to the Alexandrian dead.