Lo, he goeth out unto the water— It was most probably Pharaoh's custom to go to wash himself in the Nile, see ch. Exodus 2:5 that, after purification, he might pay the proper worship to his gods; see ch. Exodus 8:20. Some have supposed, that he went to pay his devotion to the river Nile itself, which was sacred among the Egyptians. But it is most reasonable to believe, that he went for the purpose of bathing or religious purifications.
Related Commentaries of Exodus 7:15
Exodus 7:15
15 Get thee unto Pharaoh in the morning; lo, he goeth out unto the water; and thou shalt stand by the river's brink against he come; and the rod which was turned to a serpent shalt thou take in thine hand.