The lady at the well, who comes to draw water and has this discourse with Jesus where he tells her that the water she’s come to drink will only quench her thirst temporarily, but the water he has to give her or us, will spring forth into everlasting life.
He’s referring to his word. At the end of the discourse she leaves her water pot at the well, and goes into the city and testifies to the men there that she’s found the Messiah.
This takes place at Jacob’s well, on land he gave his son Joseph, whose life is in itself a Messianic prophecy to be visited later. (John 4)