Ye gathered together the waters "And ye shall collect the waters" - There were two pools in or near Jerusalem, supplied by springs: the upper pool, or the old pool, supplied by the spring called Gihon, 2 Chronicles 32:30, towards the higher part of the city, near Sion, or the city of David, and the lower pool, probably supplied by Siloam, towards the lower part. When Hezekiah was threatened with a siege by Sennacherib, he stopped up all the waters of the fountains without the city; and brought them into the city by a conduit, or subterranean passage cut through the rock; those of the old pool, to the place where he had a double wall, so that the pool was between the two walls. This he did in order to distress the enemy, and to supply the city during the siege. This was so great a work that not only the historians have made particular mention of it, 2 Kings 20:20; 2 Chronicles 32:2, 2 Chronicles 32:3, 2 Chronicles 32:5, 2 Chronicles 32:30; but the son of Sirach also has celebrated it in his encomium on Hezekiah. "Hezekiah fortified his city, and brought in water into the midst thereof: he digged the hard rock with iron, and made wells for water," Ecclesiasticus 48.
Ye have seen also the breaches - You who are inhabitants of the city. That such breaches were actually made, see 2 Chronicles 32:5.
Of the city of David - Of Jerusalem, so called because it was the royal residence of David. Zion was usually called the city of David, but the name was given also to the entire city.
And ye gathered together - That is, Hezekiah and the people of the city collected those waters.
Of the lower pool - (For a description of the upper and lower pool, see the notes at Isaiah 7:3). The superfluous waters of the lower pool usually flowed into the valley of Hinnom, and thence, into the valley of Jehoshaphat, mingling with the waters of the brook Kedron. It would seem from the passage here that those waters were not usually retained for the use of the city, though it was possible to retain them in case of a drought or a siege. At present, the lower pool is without the walls, but Hezekiah appears to have extended a temporary wall around it so as to enclose it (see the note at Isaiah 22:11). This he did, probably for two purposes;
(1) to cut off the Assyrians from the supply of water; and
(2) to retain “all” the water in the city to supply the inhabitants during the siege; see 2 Chronicles 32:4, where it is expressly declared that Hezekiah took this measure to distress the Assyrians.