Adam Clarke on 2 Samuel 12:27

And have taken the city of waters - The city where the tank or reservoir was that supplied the city and suburbs with water. Some think that the original, לכדתי את עיר המים lachadti eth ir hammayim, should be translated I have intercepted, or cut off, the waters of the city: and Houbigant translates the place, et aquas ab urbe jam derivavi; "And I have already drawn off the waters from the city." This perfectly agrees with the account in Josephus, who says των τε ὑδατων αυτους αποτεμνομενος, having cut off their waters, Antiq., lib. vii., cap. 7. This was the reason why David should come speedily, as the citadel, deprived of water, could not long hold out.