How much water should I drink per day?

Daily water needs vary by body size, activity, and climate. General guidance: about 33 mL per kg body weight, or 2–3.5 liters for most adults. US IOM recommends 3.7 L/day total for men, 2.7 L/day for women (including water in food). EFSA (Europe) recommends 2.5 L/day for men, 2.0 L/day for women. Australia NHMRC recommends 2.6 L/day for men, 2.1 L/day for women. These are total adequate intake values — food contributes about 20%.

Is the 8 glasses per day rule accurate?

The '8 glasses per day' (8×8 rule = 64 oz ≈ 1.9 liters) is a simplification with little scientific backing. A 2002 review by Dr. Heinz Valtin in the American Journal of Physiology found no scientific evidence supporting the 8×8 rule. The correct amount depends on body weight, activity, climate, and health status. Thirst is a reliable indicator for most healthy adults.

Do different countries have different water recommendations?

Yes. The US IOM (3.7 L/2.7 L for men/women), EFSA Europe (2.5 L/2.0 L), Australia NHMRC (2.6 L/2.1 L), and Germany/Switzerland DGE (2.25 L for both sexes) all differ slightly. These are total water from all sources (beverages + food); beverages account for about 80%. The WHO does not set a specific quantity recommendation but emphasizes safe water access.

🇺🇸 US IOM 3.7L 🇪🇺 EFSA 2.5L 🇦🇺 NHMRC 2.6L 🌍 WHO

Water Intake Calculator

How much water you need depends on your body weight, activity level, and climate. Different countries' health authorities recommend different amounts — from the US IOM's 3.7 L to EFSA Europe's 2.5 L for men.

Quick Answer

~33 mL/kg body weight is a widely-used baseline. For a 70 kg adult, that's about 2.3 L/day from beverages. US IOM: men 3.7 L total, women 2.7 L total (including ~20% from food). EFSA Europe: men 2.5 L, women 2.0 L. Australia: men 2.6 L, women 2.1 L. These differ partly due to methodology — the US value includes all water from all sources.

Body weight (kg)

Activity Level

Climate / Environment

Daily Water Recommendations by Country

Authority	Men	Women	Note
🇺🇸 US IOM (National Academies)	3.7 L/day	2.7 L/day	Total water (beverages + food)
🇪🇺 EFSA (European Food Safety Authority)	2.5 L/day	2.0 L/day	Beverages only
🇦🇺 Australia NHMRC	2.6 L/day	2.1 L/day	Total adequate intake
🇩🇪 DGE / Germany / 🇨🇭 Switzerland	2.25 L/day	2.25 L/day	Beverages (no sex differentiation)
🇬🇧 UK NHS	6–8 cups (1.5–2 L)	6–8 cups (1.5–2 L)	Simplified public guideline
🇨🇦 Canada Health	~2.2 L/day	~1.9 L/day	Total adequate intake; weather-adjusted
🇯🇵 Japan MHLW	~2.5 L/day total	~2.0 L/day total	Emphasizes tea/miso soup contribution
🌍 WHO	No specific quantity	—	Focuses on water safety, not quantity

The large US IOM figure includes all water — about 20% comes from food. Comparing only beverage recommendations, estimates are more similar (~2.0–2.5 L/day).

Frequently Asked Questions

Does coffee count toward daily water intake? ▾

Yes. Despite its mild diuretic effect, coffee and tea provide a net positive contribution to hydration. A 2014 study in PLOS ONE found that moderate coffee consumption (3–4 cups/day) was equivalent to water for hydration status. The UK NHS, European EFSA, and US IOM all count caffeinated beverages in daily fluid totals. Only very high caffeine doses (>500 mg/day) may increase fluid needs slightly.

Should I drink more water when exercising? ▾

Yes. Exercise significantly increases water needs. The American College of Sports Medicine (ACSM) recommends 400–600 mL (14–20 oz) 2 hours before exercise, and 150–350 mL (6–12 oz) every 15–20 minutes during exercise. After exercise, drink enough to replace lost fluids — weigh yourself before and after to estimate: 1 kg weight loss ≈ 1 liter of sweat.

Sources & Methodology

Daily fluid recommendations reference the U.S. National Academies (IOM) adequate intake and EFSA reference values, adjusted for body weight and activity.

Standards and figures reviewed 2026.

Related Calculators

🔥 Calorie Calculator →

Daily calorie needs

⚡ BMR Calculator →

Basal metabolic rate

🍽️ Macro Calculator →

Protein, carbs and fat split

❤️ Heart Rate Calculator →

Target heart rate

Cite this page APA · MLA · BibTeX

APA

WorldCalculators.org. (n.d.). Water Intake Calculator: Daily Water by Weight & Activity. https://worldcalculators.org/calculators/water-intake/

MLA

“Water Intake Calculator: Daily Water by Weight & Activity.” WorldCalculators.org, worldcalculators.org/calculators/water-intake/.

BibTeX

@misc{worldcalculatorscalculatorswaterintake,
  title        = {Water Intake Calculator: Daily Water by Weight & Activity},
  author       = {{WorldCalculators.org}},
  year         = {n.d.},
  howpublished = {\url{https://worldcalculators.org/calculators/water-intake/}}
}

Figures change when tax years or guidance change. Cite the date shown and link the page so readers see the current version.