What Water Does
Water addresses dehydration — which is a real component of a hangover. Alcohol is a diuretic: it suppresses the hormone vasopressin, which regulates kidney water retention. The result is that you lose more water than you take in while drinking, and you sleep dehydrated.
Dehydration contributes to hangover headaches (brain volume reduction pulling on surrounding membranes), dry mouth, dizziness and fatigue. Rehydrating before bed and in the morning directly reduces these symptoms.
What Water Doesn't Do
Water cannot clear acetaldehyde any faster — the liver processes it at a fixed enzymatic rate regardless of hydration. Water doesn't replenish B vitamins. It doesn't restore REM sleep that was suppressed. It doesn't reduce inflammation or the GABA rebound effect.
This is why drinking a lot of water helps but doesn't prevent a hangover. Dehydration is one component of a multi-factorial problem.
Timing Matters
Drinking water before bed is significantly more effective than chugging it in the morning. When you sleep dehydrated, the dehydration worsens through the night — your body continues losing water through breathing and mild sweating. Starting the overnight period hydrated is better than trying to catch up at 7am.
The Optimal Approach
Water is a necessary but not sufficient hangover prevention strategy. The most effective approach pairs proper hydration before bed with a supplement that addresses the remaining causes: acetaldehyde clearance (DHM), B vitamin replenishment (B complex), liver support (milk thistle) and sleep quality (L-theanine).