Water Intake Calculator
How much water you actually need — counting the water already in your plants.
Your day
Spread this across the day rather than drinking it in a few large sittings.
How this is calculated
Baseline: the NASEM Adequate Intake for total water — 3.7 L/day for men, 2.7 L/day for women — blended with a 35 mL/kg body-weight estimate so the number tracks your size.
Exercise: about 12 mL per minute of training, which is roughly 0.4–0.8 L per hour depending on intensity.
Heat: hot or humid conditions add 10%.
Food: each serving of fruit or vegetables supplies around 120 mL. Water-dense plants — cucumber, watermelon, lettuce, tomato, celery, strawberries — sit at 90–96% water, which is why a plant-forward day genuinely reduces how much you must drink.
Worked example: a 150 lb (68 kg) woman training 30 minutes in a temperate climate with five produce servings needs about 3.0 L total; roughly 0.6 L comes from food, leaving about 2.4 L (81 oz, ten glasses) to drink.
Frequently asked
How much water should I drink a day?+
The NASEM Adequate Intake for total water is 3.7 litres a day for adult men and 2.7 litres for adult women. Roughly 20% of that normally arrives in food, so most adults need about 2.5–3 L (men) or 2 L (women) as drinks. Exercise adds about 0.4–0.8 L per hour.
Does food count toward water intake?+
Yes. Fruit and vegetables are 85–95% water — cucumber, watermelon, lettuce, tomato, strawberries, and citrus all count. Each produce serving contributes roughly 120 mL, so a produce-heavy plant-based day meaningfully lowers how much you need to drink.
Is 8 glasses of water a day correct?+
Eight 8-ounce glasses is about 1.9 L, which is a reasonable floor but not a rule. It has no clear origin in the DRI literature. Body size, exercise, and heat matter far more, which is why this calculator scales with all three.
How do I tell if I am drinking enough?+
Pale straw-coloured urine and no persistent thirst are the practical signals. Dark yellow urine, headache, or fatigue in heat suggest you are behind. Drinking to thirst works for most healthy adults; athletes and older adults, whose thirst signal blunts, benefit from a target.
Can you drink too much water?+
Rarely, but yes — consuming several litres in a short window can dilute blood sodium (hyponatraemia), which is dangerous. Spread intake across the day rather than front-loading it, and include electrolytes during long endurance efforts.
Related tools & articles
References
- Institute of Medicine. Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. National Academies Press, 2005.
- U.S. Department of Agriculture, Agricultural Research Service. FoodData Central. USDA, 2024.
Educational estimates only, not medical advice. Individual needs vary — consult a physician or registered dietitian.