Calculate Daily Water Intake

1. Enter your "Body Fat Percentage"
2. Select your "Age Group", "Activity Level", "Season", and "Purpose"
3. The "Estimated Daily Water Intake" and "Recommended Direct Water Consumption (excluding water from food)" will be displayed automatically

This tool estimates your daily water intake needs based on factors including guidelines from Japan's Ministry of Health, Labour and Welfare "Dietary Reference Intakes for Japanese (2020)" and the U.S. Institute of Medicine (IOM) water intake guidelines.

Basic Calculation Formula

Body Weight × Purpose-Specific Water Coefficient with adjustments for age, activity level, season, and gender.

• Body Weight: Input in kg
• Purpose-Specific Coefficient (mL/kg):
  • Standard: 35
  • Elderly: 30
  • Weight Loss: 45
  • Exercise Purpose: 50

Adjustment Values

• Age Adjustment: 40+ years +100mL, 60+ years +150mL
• Activity Level Adjustment: Moderate +200mL, High +400mL
• Seasonal Adjustment: Spring +100mL, Autumn +150mL, Summer +300mL
• Gender Adjustment: Male +100mL (considering muscle mass)

Recommended Beverage Intake

The calculated result represents the combined total of "water from food" and "water from beverages". Since approximately 50% comes from food for average Japanese people, drinking about Total × 0.5 as beverages provides good balance.

References

• Ministry of Health, Labour and Welfare｜Dietary Reference Intakes for Japanese (2020)
• Institute of Medicine (IOM) Report: Dietary Reference Intakes for Water
• Journal of Japanese Society of Nutrition and Food Science｜Survey on Water Intake and Dietary Content in Adults

Water is one of the most fundamental elements supporting human life. About 60% of body weight consists of water, which deeply affects cellular and organ functions. Inadequate hydration can lead to health issues, performance decline, and in worst cases, life-threatening risks.

1. Maintaining Normal Brain/Nervous System Function

About 75% of the brain consists of water. Dehydration reduces concentration, judgment, memory, and may cause headaches or dizziness.

2. Supporting Temperature Regulation

Water released as sweat helps maintain body temperature. Proper hydration is especially crucial in hot weather or during exercise.

3. Protecting Muscles and Joints

About 75% of muscles and the main component of joint lubricating fluid is water. Dehydration may cause muscle cramps or joint pain.

4. Blood Circulation and Waste Removal

Adequate water is needed to maintain blood flow and remove waste through kidneys. Insufficient water thickens blood and increases burden.

5. Promoting Digestion and Metabolism

Water is the base material for saliva and gastric juices that aid digestion. Dehydration may cause constipation, slowed metabolism, weight gain, or health issues.

Important Notes

• When you feel thirsty, mild dehydration has already begun
• Elderly and children may not notice dehydration easily - regular hydration is crucial
• Excessive water intake may burden kidney function - maintain proper amounts

Below are key research findings and basic information about water intake from Japanese Ministry of Health materials and other sources.

Water's Role in Human Body

• About 60% of human body consists of water (varies by fat-free mass)
• Water exists in intracellular fluid, plasma, interstitial fluid etc., essential for nutrient transport, waste removal, and temperature regulation
• Water balance fundamentally equals intake and excretion

Estimated Water Requirements

• Low activity level: 2.3-2.5L/day
• High activity level: 3.3-3.5L/day
• Germany sets reference values: Men 2,910mL/day, Women 2,265mL/day

Actual Measurements in Japanese (30-76 years)

• Men's average intake: 2,423g/day
• Women's average intake: 2,037g/day
• 30-49 years: 2,121g/day, 50-76 years: 2,324g/day
• Actual tap water consumption averages 1.28L/day, potential need 1.65L/day
• 88th percentile requires 2.0L/day, covering nearly everyone requires 2.5L/day or more

Intake Source Ratios

• Western countries: 20-30% from food, 70-80% from beverages
• Japanese: About 1,130g (51%) from food, 1,100g (49%) from beverages
• Reason: Higher consumption of water-rich "rice" and "noodles" compared to bread

Seasonal Water Intake Changes (Japanese Average)

Summer intake is about 200g (≈200mL) higher than winter, reflecting increased needs due to sweating.

References

• Ministry of Health, Labour and Welfare "Dietary Reference Intakes for Japanese (2020)"
• Related research: Weighed dietary record method, 24-hour urine volume survey, Internet questionnaire survey

* The natural limit (without doping) is considered to be 22-23.