ישעיהו כב:יא פירוש: רש״י ואבן עזרא

And a ditch you made A pool of water, to be a defense (lit., strength) for the city.

ומקוה And a ditch. מקוה מים ═ מקוה A gathering of water (Lev. 2:36).

between the two walls the double walls, the low wall and the high wall, and the water of the old pool.