2 Chronicles 32:2-5

When Hezekiah saw that Sennacherib had come and that he intended to go to war against Jerusalem, he decided, together with his officers and his soldiers, to stop up the water [supply] from the springs which were outside the city [by enclosing them with masonry and concealing them], and they helped him. So many people came together, and they stopped up all the springs and the brook which flowed [underground] through the region, saying, “Why should the kings of Assyria come and find an abundance of water?” Also Hezekiah resolutely set to work and rebuilt all the wall that had been broken down, and erected towers on it, and he built another wall outside and strengthened the Millo (fortification) in the City of David, and made a great number of weapons and shields.