Possible meanings are that withholding waters represents 1) preventing the rain from falling. Alternate translation: "if he stops the rain from falling the land dries up" or 2) preventing running water from flowing. Alternate translation: "if he stops the water from flowing, the land dries up" (See: [[rc://en/ta/man/jit/figs-metaphor]])
Possible meanings are that sending them out is a metaphor meaning 1) causing the rain to fall. Alternate translation: "if he causes a lot of rain to fall, it floods the land" or 2) causing the waters to flow. Alternate translation: "if he makes a lot of water flow, it floods the land" (See: [[rc://en/ta/man/jit/figs-metaphor]])