Albert Barnes Commentary Jeremiah 9:1

"Oh that my head were waters, and mine eyes a fountain of tears, that I might weep day and night for the slain of the daughter of my people!" — Jeremiah 9:1 (ASV)

This verse is joined in the Hebrew to the preceding chapter. But any break at all here interrupts the meaning.

A fountain - Rather, “a reservoir,” in which tears had been stored up, so that the prophet might weep abundantly.