Optimal water intake

For a practical starting point, use these broad guidelines and adjust for activity, heat, and your own thirst:

• At rest: Aim for about 8 oz (240 mL) of fluid per waking hour during the first 10 hours—roughly 2.4 L total. This is a general framework, not a precise requirement; fluid from beverages counts, and individual needs vary. 1
• During exercise: As a rough guide, drink body weight in pounds ÷ 30 ounces every 15–20 minutes (or 2 mL/kg over the same interval). Sip steadily if comfortable, and adjust for the exercise and your stomach. 2
• In heat or with heavy sweating: Increase exercise-fluid guidance by roughly 50–100%. If you’re parched, drink; electrolytes may be useful when you’re sweating heavily or exercising a lot. 3
• Keep it flexible: These are ballpark guides, not numbers to follow to the decimal. Food also contributes fluid, and you generally don’t need to force extra water during light activity when fluid losses are small. 4 5