How will the heat spell be like a lake?
Rashi: This is a metaphor - one who desires salvation will be saved.
Radak: The place of the heat spell and thirst will be a lake and spring that flows for them when they go in a hot, dry place. The Targum of "Achalani Chorev" (Bereishis 31:40) is Sharva.
Malbim: A place that is naturally dry will be moist.
Why does it say "b'Naveh Sanim Rivtzah"?
Rashi: In a place that was a dry Midbar, a habitat of serpents, will be a yard made for reeds. They normally grow only in a place of water - "ha'Yig'eh Gome b'Lo Vitzah" (Iyov 8:11). Rivtzah is a noun, like Marbetz, for there is no Mapik Hei 1 .
Radak: Rivtzah is a verb; each one crouches. Sanim refers also to females - "Tanim Chaltzu Shad Heniku Gureihen" (Eichah 4:3).
Perhaps the text should say for there is a Mapik Hei, or if it were a verb, there would be no Mapik Hei. Our texts have a Mapik Hei, but it seems that Rashi's text did not. (PF)
What is "Chatzir"?
Radak: Refer to 34:13:3:1.