Hydration: Facts and Myths 101

Although water has no energy capacity and is calorie-free, it is considered an essential nutrient because of the vital functions it exercises in our organism. 

Water, in fact, participates in all cellular reactions, carries the nutrients of the body, allows exchanges between the outside and inside of cells, favours the action of gastric juices (and therefore digestion), becomes part of physiological liquids and keeps the body temperature constant by means of its evaporation through the skin. These are just some of the important functions of body water which underline its value for our health.

Without water life is not possible and it is clear to everyone that drinking is crucial. Despite its well-established importance, water is often forgotten in dietary recommendations and there are so many false hydration myths about water intake and its effects on our organism.



1) Water intake and loss must be equal

Water is the major constituent of the human body which cannot produce enough water by metabolism or obtain enough water by food ingestion to fulfil its needs. 

About 60% of our body weight is made of water. This water content varies with body composition (lean and fat mass). In infants and children, water as a percentage of body weight is higher than in adults.

Under normal conditions of moderate ambient temperature (18–20 °C) and with a moderate activity level, body water remains relatively constant. This implies a precise regulation of water balance: over a 24-h period, intake and loss of water must be equal.

We can take water through liquids, and food, but we can also produce a certain amount of water. The water we drink is essentially composed of water and other liquids with a high water content (85 to 99%). The water we eat comes from various foods with a wide range of water content (40 to 48%). The water we produce results from the oxidation of macronutrients (endogenous or metabolic water).

2) Dehydration is very dangerous 

Remember, we are constantly losing water! On average, a sedentary adult loses 2–3 l of water per day. The main routes of water loss from the body are kidneys, skin, and the respiratory tract and, at a low level, the digestive system. Over a 24-h period, a sedentary adult produces 1–2 l of urine, loses water by evaporation through the skin and through the respiratory tract and about 200 ml of water a day through faeces.

The water losses through the skin and lungs depend on the climate, air temperature and relative humidity.

The intake of water is partially determined by thirst. When water losses exceed water intake, are activated a series of molecular, cellular, and hormonal mechanism, that determine the sense of thirst and induce us to drink. These mechanisms are vital, because dehydration is very dangerous to health and if prolonged it can also be dangerous for life. In case the consumption of water is not enough, there are several alarm bells. Dehydration occurs when water loss exceeds one percent of body weight with symptoms such as headache, loss of appetite, redness of the skin, dry mouth and eyes, apathy, fatigue and muscle cramps and then get to dizziness, nausea and vomiting. Dehydration also has a very negative effect on brain performance and causes lack of concentration and poor mental lucidity. You should never resist the stimulus of thirst but, on the contrary, remember to drink and increase the amount, not only when you lose more liquids, as in summer, but even in winter, when proper hydration is always fundamental for all vital functions and often the cold leads us to drink less than we will need.

3) Adult should intake 2 - 3 l per day

It is difficult to define a quantity that is good for everyone and in all situations, because, as already mentioned, climatic conditions can change (and increase sweating for example), and you can have intense sweating in case of intense physical activity. The adequate total water intakes for sedentary adults are on an average between 2 and 2.5 l per day (women and men, respectively) (EFSA, 2008). The total water inputs for sedentary adults (which also includes the water taken with food and that produced through metabolic reactions) are on an average between 2 and 3 l.

Particular attention should be paid to people at risk such as the elderly, where the stimulus of thirst is reduced, children, who due to their reduced body mass tend to lose so many fluids, sick people and not least athletes, in whom hydration should be customized according to the type and duration of physical activity.

Hydration and dehydration facts are few, but truly clear, however there are many hydration myths that often confuse ideas.


1) An excess of water makes you fat

This is absolutely false, also because, as we said at the beginning, water does not have an energy value, it is calorie-free. It is also a false hydration myth on the contrary, to think that water makes you lose weight. There is no food or drink that makes you lose weight, remember that the only valid tool we have if we want to lose fat is to follow a slightly low-calorie balanced diet associated with moderate physical activity.

2) Carbonated water it's harmful to health 

This is a classic hydration myth; it is possible to drink natural water, added with carbon dioxide or naturally sparkling. There is no indication for health, and indeed some sparkling waters can promote digestion.

3) Water helps fight fat accumulations and “orange peel skin”

Though water won’t do any harm, this is a complex inflammatory condition, and it would be too easy to heal it by drinking water!

4) It is better not to drink water during meals

This is also one of the most classic hydration myths. Water helps digestion, so it is recommended to drink it even during meals.

5) If it is hot the more water I drink the better

When it is hot it is important to increase the intake of water, because you sweat more, but drinking too much could also increase the loss of salt and lead to a much more dangerous condition of dehydration, which is hyponatremia. 

6) The calcium contained in the water makes the kidney stones

Those suffering from kidney stones can safely drink calcium-rich waters without any contraindication. The chemical form of calcium contained in water in no way contributes to the formation of these.

Do you have any other doubts about hydration facts and myths? Do not hesitate to write to us, we will answer all your questions!

Author: Francesca Deriu, Nutritionist at Minutro

Further Reading: 

E Je´quier and F Constant Water as an essential nutrient: the physiological basis of hydration European Journal of Clinical Nutrition (2010) 64, 115–123

Pross N Effects of Dehydration on Brain Functioning: A Life-Span Perspective. Ann Nutr Metab. 2017;70 Suppl 1:30-36.

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