Nutrition
As of 2026-04-24
How Water Intake Calculator works
Methodology for the Water Intake Calculator: formulas, coefficients, data sources, assumptions, and known limitations.
Scope
Estimates daily water intake from bodyweight, activity level, and climate.
Formula
water_l = bodyweight_kg * base_ml_per_kg/1000 + exercise_bonus_ml + climate_bonus_ml.
Coefficients
| Parameter | Value | Note |
|---|---|---|
| Base intake | 30–35 ml/kg/day | |
| Training bonus | +350–700 ml per hour of exercise | |
| Hot/humid bonus | +500–1000 ml/day |
Data sources
- European Food Safety Authority. Scientific Opinion on Dietary Reference Values for water. EFSA Journal. 2010;8(3):1459. — EFSA Panel on Dietetic Products, Nutrition and Allergies.
- Institute of Medicine. Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. Washington, DC: The National Academies Press, 2005. — Source of the U.S. total-water adequate-intake values.
- Sawka MN, Burke LM, Eichner ER, et al. American College of Sports Medicine position stand. Exercise and fluid replacement. Med Sci Sports Exerc. 2007;39(2):377-390. — PMID 17277604. Source of the exercise-bonus magnitudes.
Assumptions
- Total fluid intake includes water, tea, coffee, and the water content of food.
Approximation range
Individual needs vary widely with diet, climate, and medications; the tool outputs a starting range, not a prescription.
Limitations
- Not appropriate for people on fluid-restriction regimens (heart failure, kidney disease).
- Cannot model acute sweat loss — use the Sweat Rate Calculator for session-specific hydration.
Reproducibility
80 kg, moderate activity, temperate climate: 80 * 32.5 ml = 2600 ml base + 500 ml exercise = ~3.1 L/day.
Change log
- 2026-04-24: methodology page first published.
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