The city of waters - The lower town of Rabbah (the modern Ammam), so called from a stream which rises within it and flows through it. The upper town with the citadel lay on a hill to the north of the stream, and was probably not tenable for any length of time after the supply of water was cut off.
Related Commentaries of 2 Samuel 12:27
2 Samuel 12:27
27 And Joab sent messengers to David, and said, I have fought against Rabbah, and have taken the city of waters.