Surah 56:68–70:
Have you seen the water that you drink? Is it you who brought it down from the rainclouds, or is it We who bring it down? If We willed, We could make it bitter, so why are you not grateful?
In a series of rhetorical challenges designed to humble humanity, verses 68–70 ask the listener if they are the ones who bring fresh water down from the rainclouds (al-muz'n), warning: "If We willed, We could make it bitter [salty]."
The Hydrological Reality:
To an atmospheric scientist, this cosmic threat betrays a fundamental ignorance of the physical laws governing the global water cycle. Rain clouds are formed through evaporation. When solar energy heats the oceans, water transforms into vapor, leaving all dissolved salts and minerals behind in the sea. This natural distillation process ensures that water vapor is always purely fresh before it condenses into clouds.
The Cosmic Mixer Model:
For a cloud to dump heavily salinated, bitter marine water directly onto land as rain is a thermodynamic impossibility. The text operates on a primitive, pre-scientific "Rainmaker" model. It assumes that God manually pumps water from an undifferentiated reservoir in the sky and can choose to open a "salt valve" or a "fresh valve" at will, entirely unaware of the self-purifying mechanics of evaporation.