Most adults wake mildly dehydrated from overnight respiration. Coffee further dehydrates. Drinking 250-500ml water first thing — before coffee — establishes hydration baseline that's easier to maintain through the day.
Simple implementation
Full glass of water on bedside table or kitchen counter. Drink immediately on waking. Then coffee, breakfast, day.
What this does
Replaces overnight water loss. Mild appetite suppression. Improved cognitive function within minutes. Establishes hydration anchor.
Five seconds; meaningful effect on daily hydration and energy.