Water in your body

Water: The Major component of the Human Body

On average, the body of an adult human being contains 60% water. Most of the water in the human body is contained inside our cells. In fact, our billions of cells must have water to live.

The total amount of water in our body is found in three main locations: within our cells (two-thirds of the water), in the space between our cells and in our blood (one-third of the water). For example, a 70-kg man is made up of about 42L of total water.

28 litres is intracellular water

14L is found in extracellular fluid 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), which is an aqueous medium surrounding cells. (1)

Actually, the amount of water a body contains varies according to certain contexts: The body of a newborn is composed of more water (75%) than that of an elderly person (50%). Also, the more muscular a body is, the more water it contains. Conversely, the more fat in the body, the less water the body contains – as body fat has little water.

Also, all our vital organs contain different amounts of water: the brain, the lungs, the heart, the liver and the kidneys contain a large quantity of water – between 65 to 85% depending on the organ (2), while bones contain less water (but still 31%!).

For all those reasons, 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.

The Functions of Water

Water is involved in many of our body’s vital functions

Water is a carrier, distributing essential nutrients to cells, such as minerals, vitamins and glucose.

Water removes waste products including toxins that the organs’ cells reject, and removes them through urines and faeces.

Water participates in the biochemical break-down of what we eat.

Water has a large heat capacity which helps limit changes in body temperature in a warm or a cold environment. Water allows the body to release heat when ambient temperature is higher than body temperature (1). The body begins to sweat, and the evaporation of water from the skin surface very efficiently cools the body.

Water is an effective lubricant around joints. It also acts as a shock absorber for eyes, brain, spinal cord and even for the foetus through amniotic fluid.

Water is at the centre of life. This is why nobody can live more than 3 to 5 days without any water intake.

Source:
Montain et al. (1999). Mil Med 164 : 502-508