To stop the waters ... - Compare 2 Chronicles 32:30. Hezekiah’s object was probably twofold - to hide the springs outside the city in order to distress the Assyrians, and to convey their water underground into the city, in order to increase his own supply during the siege.
Related Commentaries of 2 Chronicles 32:3
2 Chronicles 32:3
3 He took counsel with his princes and his mighty men to stop the waters of the fountains which were without the city: and they did help him.