2 Chronicles 32:4
So there was gathered much people together, who stopped all the fountains, and the brook that ran through the midst of the land, saying, Why should the kings of Assyria come, and find much water? So there was gathered much people together, who stopped all the fountains, and the brook that ran through the midst of the land, saying, Why should the kings of Assyria come, and find much water?
Hezekiah carried out the stopping of the waters while Judah was still paying tribute under the agreement made in the time of Ahaz, using the interval before Samaria fell to strengthen Jerusalem for the coming conflict. He did not act alone but after counsel with his princes and his mighty men, deliberately planning how the city could endure a siege. The decision was to secure a bountiful supply of water inside the walls of Jerusalem while producing scarcity outside the city, so that the kings of Assyria when they came would find no water to sustain a besieging army.
Stopping the fountains and the brook that ran through the midst of the land was only one part of a larger program of human preparation. Together with it he rebuilt the broken portions of the wall, raised up towers upon it, built another wall outside the first, repaired Millo in the city of David, made darts and shields in abundance, and set captains of war over the people. In all this he did everything that human ingenuity and energy could devise for the defense of Judah against Assyria. When that completed human work was done, he joined to it an exhortation to the people to be strong and of good courage, because the Lord God was with Judah to help and to fight its battles.