When will the poor seek water?
Rashi: This is a Nevu'ah about the end of days. "Lo Ra'av la'Lechem v'Lo Tzama la'Mayim Ki Im Lishmo'a Divrei Hashem" (Amos 8:11). People will go around to find Devar Hashem, and not find it. When His anger departs, He will prepare for them bread and water, and make His Shechinah dwell and put Ru'ach in their Nevi'im's mouths.
Radak: When they return from Galus via Midbaros, where there is no water. They will seek water and not find it. Their tongue will be dry from thirst. They will scream to Me, and I will answer them, for I am Elokei Yisrael. I took them out of Galus; I will not abandon them to die of thirst in the Midbar!
Malbim: Yisrael in Galus despaired of redemption for two reasons. (a) They saw that they are weaker than their strong and numerous captors. Therefore, it says "Al Tira Tola'as Yakov" (14). (b) Due to poverty [they despaired]. Therefore, it says that the Aniyim, and even the Evyonim (who are more destitute), who seek water, which is cheap, their tongues are dry
What is the meaning of "Nashatah"?
Rashi: It is like "v;Nishesu Mayim meha'Yam", "ha'Sheis veha'Shaver" (Eichah 3:47). All are expressions of desolation and dryness. There is a Dagesh in the Tov, for it is in place of an extra Sov, for Sheis always has a Sov, and it should say Nashasasah, for it is feminine.
Radak: This is like "Nashsah Gevurasam" (Yirmeyah 51:30). The Dagesh in the Tov is due to the Asnachta.
Why does it say "Hashem" and "Elokei Yisrael"?
Malbim: I am Hashem, who created everything, so I will answer them. I am Elokei Yisrael, based on their good deeds. They will not need to pray at all, for I will not abandon them! One who must pray was abandoned, to the point that he needed to pray!
