John Gill's  Exposition of the Bible 

2 Kings 20:20

And the rest of the acts of Hezekiah, and all his might, and how he made a pool, and a conduit, and brought water into the city, are they not written in the book of the chronicles of the kings of Judah?

And the rest of the acts of Hezekiah, and all his might,.... Which he exerted in his wars with his enemies, and in the reformation of religion, and abolition of idolatry:

and how he made a pool, and a conduit, and brought water into the city; at the same time that he cut it off from the enemy without, see

2 Chronicles 32:3,

are they not written in the book of the chronicles of the kings of Judah? a book often referred to in this history, but since lost; many of his acts are recorded in the canonical book of Chronicles, 2 Chronicles 29:1.