Hydration is key to bodily function in *many* (if not most ways). Without water, there’s no blood (and a million other watery things inside us). With no blood, the heart (powered by electrical signals facilitated by electrolytes/etc, which depends on a balance of hydration) has nothing to do. With nothing to do, the heart stops, which leads to the brain (also dependent on water and blood and electrical signals) shutting down, followed by cessation.
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