1)
What is the significance of the water going over his head?
1.
Rav Sadya Gaon: When it went [over my head, I said Nigzarti].
2.
Rashi: When one is in water up to his loins, he still has hope. When it goes over his head, he loses hope. I did not do so, rather, "Karasi" (55). The "water" is the nations.
3.
Ri Kara: It was a deep pit from which I could never leave. Further, they also threw rocks at me. And additionally, there was water in it over my head. I could have lost hope. Even so, I did not lose hope from my Creator.
4.
Palgei Mayim: In this Galus, afflictions grew so much, like water over my head, to the point that I said Nigzarti.