Hydration for running: how much to drink before, during and after.

Hydration is not one-size-fits-all

Two people can run together at the same pace and temperature yet lose very different amounts of sweat. Body mass, intensity, acclimatization, clothing, humidity and individual physiology all matter. Modern guidance therefore favors an individualized plan that limits excessive loss without trying to replace every drop at any cost.

The goal is not to drink as much as possible. It is to finish without excessive fluid loss—and without consuming more than your body has eliminated.

Before running: begin in balance

On most days, regular meals and fluids are enough. Persistent dark urine, strong thirst and many hours without drinking suggest correcting hydration earlier instead of taking a large volume just before leaving. The American College of Sports Medicine offers 5–7 mL per kilogram of body mass in the four hours before exercise as a reference when specific preparation is needed—about 350–490 mL for a 70 kg runner.

During the run: duration and weather change the decision

Many people can complete a short, easy run in mild weather using normal daily hydration and thirst. As a session becomes longer, hotter or harder, access to fluids matters more. Do not copy another runner’s plan: test a comfortable range in training and rehearse the strategy before race day.

Estimate your sweat rate

Weigh yourself in dry clothing before and after a timed session, record everything you drink, add the body-mass loss to the fluid consumed, and divide by the duration. Losing 0.7 kg while drinking 300 mL in one hour suggests roughly 1.0 L of loss in those conditions. Heat, humidity, pace and clothing can change the result substantially.

What about electrolytes?

Sodium helps retain ingested fluid and becomes more relevant during long exercise or heavy sweating. The International Olympic Committee notes that about 0.5–0.7 g of sodium per liter may be part of the plan for many athletes exercising for more than an hour in the heat. That does not mean every run requires a sports drink; water is sufficient for many shorter sessions.

Too much fluid can also be dangerous

Exercise-associated hyponatremia can occur when blood sodium falls, often during prolonged events with fluid intake above the body’s ability to eliminate it. Electrolyte drinks do not cancel the risk if total volume is excessive. Finishing heavier than you started is a warning; severe headache, nausea, confusion, swelling or altered mental status requires immediate medical evaluation.

Afterwards: recover gradually

After an ordinary run, drinking to thirst and eating a normal meal usually helps restore fluid, sodium and energy. When losses were high or another session is close, monitor body-mass change and replace gradually with food. Use thirst for short easy runs, test sweat-based volumes in long sessions, adjust expectations in heat, and never try a new race strategy on race day.