Matthew Poole and continuators on Isaiah 22:9

9 Ye have seen also the breaches of the city of David, that they are many: and ye gathered together the waters of the lower pool .

i. e. Observed or confidered, as this Word is used, Exod. 32. 9. and elsewhere, in order to the Reparation of them, and to fortifie the City, as the next Words manifest.

That you might both deprive the Enemy of Water, and supply the City with it; of which see on 2 Chron. 32. 4, 5.