The importance of hydration

Water: an essential nutrient for life

Often overlooked as a nutrient, water is nevertheless the most essential element for the proper functioning of our bodies. It accounts for approximately 60% of body weight, or about 42 liters for a 70 kg adult. This percentage varies with age: infants have a higher body water content than adults, while it gradually decreases in older people. However, good hydration remains essential at all ages.

Most of this water, about two-thirds, is found inside our cells: this is intracellular water. The remaining third is distributed in the extracellular fluid, which includes blood plasma, interstitial fluid, and the lymphatic system.

Water plays a fundamental role in the countless chemical reactions that take place continuously in our bodies. Combined with minerals and trace elements, it enables the enzymatic reactions that are essential for life to take place. Without water, there would be no enzymatic reactions and therefore no life.

But its functions do not stop there. Water also ensures the transport of nutrients and oxygen to cells, facilitates the elimination of metabolic waste, supports exchanges between the intra- and extracellular environments, participates in the digestive process, and plays a crucial role in regulating body temperature.

In fact, our metabolism is far from being perfectly energy efficient: nearly 75% of the energy produced during the breakdown of nutrients is released as heat. Without an effective cooling mechanism, such as perspiration, our bodies would quickly overheat. Here again, water is at the heart of the system. [1, 2]

 

Why is hydration essential?

Drinking enough water is not just a matter of comfort, it is a vital necessity. Good hydration helps to:

  • optimize the use of energy from food,
  • facilitate the elimination of waste produced by the body,
  • maintain the quality of tissues such as skin and hair,
  • transport oxygen and nutrients efficiently to cells,
  • regulate body temperature.
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Water plays such a central role that even a slight decrease in our fluid reserves can have visible repercussions. Even moderate dehydration can lead to fatigue, constipation, loss of appetite, drowsiness, concentration problems, decreased alertness, or even agitation...[1, 2]

 

Our daily water requirements

Every day, our bodies renew a significant portion of their water to compensate for natural losses.

On average, we eliminate:

  • 1.3 to 1.5 liters through urination and bowel movements
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  • 0.7 to 1 liter through breathing and perspiration.

In total, this represents more than 2.5 liters of water that must be replaced daily to maintain water balance.

This water comes from three sources:

  • Metabolic water: produced by the body's enzymatic reactions, approximately 10% of intake, or 0.3 L.
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  • Water contained in food: approximately 0.8 L.
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  • Drinking water (all forms combined): more than 1.5 liters, essential for covering our needs, not including the additional hydration required during physical activity.[3]
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How to stay hydrated?

Water is essential for our balance, and to ensure that the body functions properly, it is recommended to drink between 1.5 and 2 liters of water per day. This amount may of course vary depending on age, physical activity, climate, and health, but regular intake remains essential, even if you don't feel thirsty.

It is advisable to spread your water consumption throughout the day, without waiting until you feel thirsty, as this sensation often comes late and can be altered, especially in older people. The ANSES (French Agency for Food, Environmental and Occupational Health & Safety) recommends a minimum water intake of 1.5 liters per day for adults, specifying that certain mineral waters rich in sodium should be consumed in moderation, as they may have contraindications. [4]

Many people tend to drink more during meals. However, drinking large amounts of water at this time can dilute digestive juices and disrupt digestion. It is therefore better to adopt a hydration strategy spread throughout the day.

Here is an example of a simple routine to follow:

  • A large glass of water upon waking to kick-start the body;
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  • Two large glasses in the morning (about 500 ml);
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  • One to two small glasses during lunch;
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  • Two large glasses in the afternoon;
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  • One to two small glasses during dinner.
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Water remains the best choice, whether still or sparkling. Herbal teas, tea, and unsweetened coffee can also contribute to hydration. However, be careful with fruit juices, which are often very sugary and should be consumed in moderation.

 

Certain situations increase our need for water

Our water needs are not always constant. Certain situations, whether physiological or environmental, lead to increased water loss and therefore require adequate hydration.

Here are the main circumstances that require increased vigilance:

  1. Significant loss of body fluids
  2. In cases of diarrhea, vomiting, or burns, the body loses a significant amount of water. These losses must be quickly compensated for to avoid severe dehydration.
  3. Aging
  4. With age, the sensation of thirst diminishes and the internal mechanisms for detecting dehydration become less effective. This is why older people must be particularly attentive to their fluid intake, even if they do not feel thirsty.
  5. Physical activity
  6. During muscular exertion, particularly during sports activities, water loss through perspiration increases. It is generally recommended to drink about 500 mL of water per hour of exercise, depending on the intensity and weather conditions.
  7. Heat and humidity
  8. In hot, humid weather, sweating is more profuse, even at rest. It is therefore essential to increase your water intake and adapt it to your level of exposure and sweating.
  9. Fever or infection
  10. When body temperature rises, water requirements increase. On average, it is advisable to add about 300 mL of water for every degree above normal temperature.
  11.  

In conclusion: drink to live better

Water is not just something we drink with our meals, it is a real pillar of our health. Present in every cell and involved in all major biological processes, it is essential for our energy, concentration, digestion, thermoregulation, and much more.

Staying properly hydrated is a simple but fundamental part of everyday life. Drinking regularly, without waiting until you are thirsty, and adapting your intake to your current needs (age, physical activity, outside temperature, state of health, etc.) are reflexes that support the proper functioning of our bodies.

At a time when we often seek complex solutions to improve our vitality or mental clarity, it is good to remember that something as basic as drinking water can have a profound impact.

In short, hydration is not a detail... it is a priority!

 

Sources:

[1] Popkin, Barry M., et al. “Water, Hydration and Health.” Nutrition Reviews, vol. 68, no. 8, Aug. 2010, pp. 439–58, https://doi.org/10.1111/j.1753-4887.2010.00304.x.

[2] Riebl, Shaun K., and Brenda M. Davy. “The Hydration Equation: Update on Water Balance and Cognitive Performance.” ACSM’s Health & Fitness Journal, vol. 17, no. 6, 2013, pp. 21–28, https://doi.org/10.1249/FIT.0b013e3182a9570f.

[3] Convertino, Victor A., et al. “ACSM Position Stand: Exercise and Fluid Replacement.” Medicine & Science in Sports & Exercise, vol. 28, no. 10, Oct. 1996, p. i, https://journals.lww.com/acsm-msse/fulltext/1996/10000/acsm_position_stand__exercise_and_fluid.45.aspx.

[4] ANSES: “Drinking water: best practices.” Accessed August 12, 2025. Available at https://www.anses.fr/fr/content/boire-de-leau-les-bonnes-pratiques