1)
What water would have flooded us?
1.
Radak: This is a metaphor for afflictions.
2.
Malbim: When they did not want to destroy us amidst anger, rather, just the contrary, they wanted to draw us close to be one nation [with them. This is a metaphor for] destroying our souls.
2)
What is "Nachlah"?
1.
Rashi: It is an expression of Choli (illness).
2.
Radak: It is a flooding river. The Hei at the end is extra. This is like "Nachlah Egypt" (Bamidbar 34:5).