Charles Ellicott Commentary Genesis 21:19

"And God opened her eyes, and she saw a well of water. And she went, and filled the bottle with water, and gave the lad drink." — Genesis 21:19 (ASV)

A well of water. —Not a cistern, but a spring of living water. The mirage in the desert so wearies the traveler, 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 around the spring, or some vegetation.