En-rogel

fountain of the treaders; i.e., "foot-fountain;" also called the "fullers' fountain," because fullers here trod the clothes in water. It has been identified with the "fountain of the virgin" (q.v.), the modern 'Ain Ummel-Daraj. Others identify it, with perhaps some probability, with the Bir Eyub, to the south of the Pool of Siloam, and below the junction of the valleys of Kidron and Hinnom. (See FOUNTAIN)

It was at this fountain that Jonathan and Ahimaaz lay hid after the flight of David (2Sam 17:17); and here also Adonijah held the feast when he aspired to the throne of his father (1Kings 1:9).

The Bir Eyub, or "Joab's well," "is a singular work of ancient enterprise. The shaft sunk through the solid rock in the bed of the Kidron is 125 feet deep...The water is pure and entirely sweet, quite different from that of Siloam; which proves that there is no connection between them." Thomson's Land and the Book.

EBD - Easton's Bible Dictionary