Jamieson, Fausset and Brown on Numbers 21:17-18

17-18. Then Israel sang--This beautiful little song was in accordance with the wants and feelings of travelling caravans in the East, where water is an occasion both of prayer and thanksgiving. From the princes using their official rods only, and not spades, it seems probable that this well was concealed by the brushwood or the sand, as is the case with many wells in Idumea still. The discovery of it was seasonable, and owing to the special interposition of God.