On average, the body of an adult human being is 60% water, most of which is contained in the cells, which need water to live.
Water − the human body's major component
The water in our body is found in two main locations, in our cells (two-thirds) and outside our cells (one-third).
The body of a 70-kg man, for example, contains about 42L of water − 28L intracellular and 14L extracellular, of which:
- 3L is blood plasma;
- 1L is the transcellular fluid (cerebrospinal fluid, ocular, pleural, peritoneal and synovial fluids);
- 10L is the interstitial fluid (including lymph) − an aqueous medium surrounding the cells(1).
The amount of water in a human body varies according to age. The body of a newborn, for example, is composed of more water (75%) than that of an elderly person (50%).
Sources: Mentes J. Oral hydration in older adults. AJN 2006: 106 (6):40-49 ; Jéquier et al. Water as an essential nutriment: the physiological basis of hydration. EJCN 2010: 64:11-23.
Also, the more muscular a body is, the more water it contains. Conversely, the more fat there is in the body, the less water will be present.
Our vital organs, too, are made up of different amounts of water. The brain, lungs, heart, liver and kidneys contain a lot of water − between 71% and 84%, depending on the organ(2). Even our bones are 31% water!
So, as you can see, water is life!
Sources: (1) Wang et al. (1996). Am J Clin Nut 69: 833-841; (2) Mitchell et al. The Journal of Biological Chemistry, 1945: 625-637