The best-known myth identifies Aquarius with Ganymede, a beautiful youth with whom Zeus fell in love, and whom he (in the guise of an eagle, represented as the constellation Aquila) carried off to Olympus to be cupbearer to the gods. Crater is sometimes identified as his cup.

Aquarius generally resembles the figure of a man, and when considering fainter humanly visible stars, it takes on the image of a man with a bucket from which is pouring a stream. Aquarius was also identified as the pourer of the waters which flooded the earth in the Great Flood, in the ancient Greek version of the myth. As such, the constellation Eridanus was sometimes identified as being a river poured out by Aquarius.

It may also, together with the constellation Pegasus, be part of the origin of the myth of the Mares of Diomedes, which forms one of The Twelve Labours of Heracles. Its association with pouring out rivers, and the nearby constellation of Capricornus, may be the source of the myth of the Augean stable, which forms another of the labours