Hydration: How Much Water Should You Drink Per Day?

Why Water Is Essential to the Body

The human body is composed of 60 to 70% water. It plays a role in virtually all biological functions: temperature regulation, nutrient transport, waste elimination, joint lubrication, and proper brain function. Dehydration of just 1 to 2% of body weight is enough to cause fatigue, difficulty concentrating, and headaches.

How Much Water Per Day? Official Recommendations

Major health organizations recommend:

Note: total intake includes water from foods (fruits, vegetables, soups), which accounts for approximately 20 to 30% of daily intake.

The Formula to Calculate Your Personal Needs

A simple estimate: 35 ml × your weight in kg. That's 2.45 L for a 70 kg person. Adjust based on:

• Physical activity: +500 ml to +1.5 L depending on intensity and duration
• Heat: +500 ml to +1 L per 10°C above 20°C
• Altitude: +500 ml above 2,500 m
• Illness / fever: +150 ml per degree of fever
• Pregnancy: +300 ml / breastfeeding: +700 ml

Signs of Dehydration to Watch For

The body sends signals well before dehydration becomes dangerous:

• Dark urine (amber yellow or darker): the most reliable sign — aim for pale straw yellow
• Thirst: a late signal, you're already slightly dehydrated
• Unexplained fatigue and decreased concentration
• Headaches (often tension-related, linked to dehydration)
• Dizziness when standing (orthostatic hypotension)
• Dry mouth, chapped lips
• Muscle cramps during exercise

Water or Other Drinks? What Really Matters

All beverages contribute to hydration, but not equally:

Practical Strategies to Drink More

Many people don't drink enough out of habit rather than lack of time. Here are strategies that work:

• Start the day with a large glass of water (400 ml) upon waking, before coffee
• Keep a visible 500 ml bottle on your desk — you'll empty it 4 times without thinking
• Link water to routines: a glass before each meal, a glass after each bathroom visit
• Flavor your water with a slice of lemon, cucumber, mint leaves — if you find plain water boring
• Use an app (Nutrya) for personalized reminders throughout the day
• Eat more fruits and vegetables: cucumber (97% water), tomato (95%), melon (90%), strawberry (91%)

Hydration and Sport: Before, During, After

Dehydration is the primary factor in reduced athletic performance. Even 2% dehydration reduces muscle strength by 10% and endurance by 20 to 30%.

• Before training: drink 400 to 600 ml in the 2 hours before exercise
• During exercise: 150 to 250 ml every 15 to 20 minutes (depending on intensity and heat)
• After exercise: weigh yourself before/after — drink 1.5 L for each kg lost during exercise
• Isotonic drinks: useful only for efforts lasting more than 60–90 minutes — otherwise water is sufficient

Hydration and Weight Loss

Water supports weight loss through several mechanisms:

• Satiety effect: drinking 500 ml of water 30 minutes before a meal reduces food intake by about 13% (Clinical Nutrition study, 2015)
• Thermogenesis: drinking cold water slightly increases metabolism (+30 kcal/L)
• Hunger/thirst confusion: 37% of people mistake the thirst signal for hunger — drinking a large glass before snacking reduces false cravings
• Lipid metabolism optimization: lipolysis (fat breakdown) requires water as a reactant

Can You Drink Too Much Water?

Yes, in extreme cases. Hyponatremia (excess water diluting blood sodium) is a real risk for ultramarathoners drinking pure water without electrolytes for several hours. For a normal person, kidneys can eliminate up to 1 liter of water per hour. Staying below this threshold is perfectly safe. Aim for 200 to 400 ml per hour rather than large amounts at once.

Frequently Asked Questions About Hydration

Do coffee and tea dehydrate you?

Myth! Although caffeine is slightly diuretic, the effect is offset by the water in the drink. Tea and coffee count toward your daily water balance. Only excessive consumption (more than 5 cups of coffee per day) may have a slight net diuretic effect.

Should you drink before feeling thirsty?

Yes, especially for older adults and athletes. The feeling of thirst appears when you've already lost 1 to 1.5% of your body water. Older adults have a reduced sense of thirst, making them more vulnerable to chronic dehydration. Drinking regularly without waiting for thirst is the best strategy.

Does sparkling water hydrate as well as still water?

Yes, studies show no difference in hydration between still and sparkling water. Sparkling water may even be slightly more filling thanks to CO₂. The only downside: some sensitive people may experience bloating. Sparkling water is slightly more acidifying (pH ~5-6) but with no clinical impact on the body.

Can Nutrya help me track my hydration?

Yes. Nutrya includes a hydration tracker with customizable reminders based on your profile (weight, activity, wake-up time). The app automatically calculates your daily goal and sends notifications at regular intervals to maintain optimal hydration throughout the day.