How much water is there in the human body?

Answer to this question: it depends! The proportion decreases during life, from 80% of the fetus to 50% of the elderly. Between the two, the adult woman retains about 55% and a man rather 60%. And inside the body, the amount varies widely depending on the tissue.

The proportion of water in the human body, expressed as a percentage of the mass body, is around 60% in adults, the figure varying according to sources. It's a lot since it represents more than 40 liters for a person of 70 kg but the proportion is even lower than that of the tomato and that of the astonished, which reach 95%. Life was born in water and, four billion years later, this atavism has not disappeared.

The value also varies between individuals and over the course of life. In the womb, the fetus is 80% water. The infant descends to around 75% and the proportion then depends on the gender. In adult men, it is close to 60%, or slightly more. In women, it is closer to 55% because the body door more of adipose tissue, poor in water, and slightly less muscle. Then, in one as in the other, the figure decreases to around 50% for an elderly person.

Two and a half liters of water to be renewed daily

Most of this water is contained in our cells. They are small but numerous: around 1013 (10,000 billion). There are also some in the interstitial tissues, in the blood and in all the tissues, with a very uneven distribution. Here are some examples :

  • Blood: 79%;

  • lungs: 78%;

  • brain: 76%;

  • muscles: 75%;

  • skin: 70%;

  • bone: 22.5%;

  • adipose tissue: 10%;

  • teeth: 1% (source: CNRS).

This water is more or less regularly completely renewed. Every day, the human body eliminates about 2.5 liters of water through respiration, sweat, urine … It is therefore necessary to replace this volume through food and drink, whose daily intakes are respectively (and approximately) 1.5 and 2 liters.

This molecule (H2O) plays countless roles. It is first a solvent liquid, which allows chemical reactions complexes on which life is based. Even if exobiologists dare to consider it, life without liquid water seems difficult to conceive. In any case, life as we know it.

© Shutterstock