When the poor and needy seek water, and there is none, and their tongue faileth for thirst, I the LORD will hear them, I the God of Israel will not forsake them.
(When) the poor and needy - primarily the exiles in Babylon.
Seek water - fig., refreshment, prosperity after their affliction. The language is so constructed as only very partially to apply to the local and temporary event of the restoration from Babylon; but fully to be realized in the waters of life and of the Spirit under the Gospel (Isaiah 30:25; Isaiah 44:3; John 7:37-39; John 4:14). God performed no miracles that we read of, in any wilderness, during the return from Babylon.
And their tongue faileth - is rigid or parched (Horsley).