How Much Water Do You Need When Exercising?

Losing just 2% of your body weight through sweat can slash your endurance by up to 10%. That's about 1.4 liters for a 70 kg person—an amount you can easily lose during a single hour of moderate-to-vigorous exercise on a warm day. Most gym-goers and runners know they should hydrate. Fewer know how much, when, and what happens when they get it wrong. This guide gives you the specifics. What Happens When You Exercise Dehydrated Your body cools itself primarily through sweat. During exercise, core temperature rises and sweat rates increase to dissipate heat. When fluid intake doesn't keep pace with fluid loss: - Heart rate climbs. Less blood volume means your heart pumps faster to deliver the same amount of oxygen. - Perceived effort increases. The same workout feels harder. - Performance drops. Endurance, strength, and reaction time all decline measurably. - Heat illness risk rises. Without adequate cooling, you're vulnerable to heat exhaustion or worse. How Much to Drink: Before, During, and After Before Exercise (Pre-Hydration) - 2–4 hours before: Drink 5–7 ml per kg of body weight. For a 75 kg person, that's 375–525 ml. - 15–30 minutes before: Sip another 200–300 ml. Check your urine color. Pale yellow means you're ready. Dark amber means you need more time and fluid. During Exercise - General guideline: 150–350 ml every 15–20 minutes. - Endurance sessions (60+ min): Include electrolytes, especially sodium. - High-heat conditions: Lean toward the higher end of that range. After Exercise (Rehydration) Weigh yourself before and after exercise. For every kilogram lost, drink 1.25–1.5 liters over the following 2–4 hours. Hydration by Exercise Type Estimated additional water needed per hour: - Walking (moderate): 400–600 ml - Running (moderate): 800–1,500 ml — See running hydration guide - Cycling: 700–1,200 ml — See cycling hydration guide - Swimming: 400–800 ml — See swimming hydration guide - Weight training: 500–1,000 ml — See workout guide - HIIT: 900–1,500 ml - Yoga: 300–600 ml — See yoga hydration guide Our water intake calculator includes an "Activity → Extra Water" mode that calculates additional hydration needs based on your specific activity, duration, and intensity. For pre-workout preparation, see our guide on water before workouts. When Do You Need Electrolytes? Water alone is sufficient for workouts under 60 minutes in moderate conditions. Beyond that threshold: - Sodium prevents hyponatremia and aids fluid retention - Potassium supports muscle f…