How much water should you really drink each day? Enter your weight, activity level, and climate to get a science-based hydration recommendation. Track your progress with our built-in glass counter.
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Water makes up about 60% of your body weight and is essential for virtually every bodily function: regulating temperature, transporting nutrients, cushioning organs, lubricating joints, and flushing waste. Even mild dehydration (1–2% of body weight) can impair concentration, increase fatigue, trigger headaches, and reduce exercise performance by up to 25%. Chronic mild dehydration is surprisingly common and often mistaken for hunger or tiredness.
The old "8 glasses a day" rule is a rough approximation. Actual needs vary significantly based on body weight, activity level, climate, and diet. A general guideline is to drink half your body weight in ounces (e.g., a 160-lb person needs about 80 oz). Active people, those in hot climates, pregnant or nursing women, and people at high altitudes need more. About 20% of daily water intake typically comes from food, especially fruits and vegetables.
The simplest hydration check is urine color: pale yellow means well-hydrated, dark yellow or amber suggests dehydration. Other signs include thirst (which actually lags behind actual dehydration), dry mouth, fatigue, dizziness, and decreased urine output. During exercise, weigh yourself before and after — each pound lost represents about 16 oz of water that needs replacing. Sipping water throughout the day is more effective than drinking large amounts at once.