Genesis 21:19 - Ellicott's Commentary On The Whole Bible

A well of water. — Not a cistern, but a spring of living water. The mirage in the desert so wearies the traveller, that at last he turns in despair from what may be more truthful signs. But after her outburst of grief, Hagar would grow more calm, and, encouraged by the angel’s voice, she renews her search, and finds. As Abravanel notices, the well already existed, and was not created for Hagar’s use; for God, it is said, opened her eyes, that is, enabled her to see something that indicated the existence of water: trees probably rising round the spring, or some vegetable upgrowth.