Passage 8.18.3
ἐποίησε δὲ καὶ ἐν Ἅιδου ὕδωρ εἶναι, καὶ Ἀθηνᾶ τὸν Δία οὐ μεμνῆσθαί φησιν ὅτι διʼ αὐτῆς Ἡρακλέα ἔσωζεν ἐκ τῶν Εὐρυσθέως ἄθλων· εἰ γὰρ ἐγὼ τόδε ᾔδη ἐνὶ φρεσὶ πευκαλίμῃσιν, εὖτέ μιν εἰς Ἀίδαο πυλάρταο προὔπεμψεν ἐξ Ἐρέβευς ἄξοντα κύνα στυγεροῦ Ἀίδαο, οὐκ ἂν ὑπεξέφυγε Στυγὸς ὕδατος αἰπὰ ῥέεθρα. Homer, unknown location.
He also represented water as existing in Hades, and Athena says that Zeus did not remember how she had saved Heracles many times during the labors assigned by Eurystheus: "For had I known this in my prudent mind, at the time when he sent him forth from Erebus to the gatekeeper of Hades, to fetch the hound of dread Hades, he would never have escaped the steep-flowing currents of the water of Styx." Homer, unknown location.