The Down Low on H2O

We human beings are all roughly 66.666% H2O (water).

It makes up about three-quarters of our lean body mass, about 10% of our fat, and in terms of the amount of time we could live without consuming it, water is the most essential of our nutrients.  An interesting article from Medical News Today sheds more light on this subjective subject, as there are certainly many mixed opinions on how much water is truly necessary for our bodies on a daily basis.

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But exactly how much water should we be taking in each day?

You might expect science to have provided a reliable answer to such a question – water is a fundamental constituent of life, after all.

But with the highly evolved ability of the human body to regulate water so exquisitely – and with lots of individual variability in the optimum intake – there is no definitive answer for the amount of water one person or another should get each day.

In fact, the best guidance is simply to follow the natural call of the body when more fluid is needed … JUST FOLLOW YOUR THIRST.

Yet the question of amount persists, and there is misinformation in abundance.  Vested interests come up with highly questionable ideas about how we should all be drinking more water.  Even well-respected sources cite daily intake amounts that lack good scientific evidence to support them.  A large proportion of the human body consists of water, with the exact proportion depending on factors such as age and fitness.

The principal chemical making up the human body is water (H2O), roughly comprising two-thirds of the body because humans show considerable variability in body composition.  The average young man has a percentage water composition anywhere between 50-70% of their body weight.  A similar range is seen between early and later years – infants have 75% of their body weight accounted for by water, whereas the proportion in older people is just 55%.

Recommended Daily Water Intake

The “adequate intakes” officially recommended for total water from all sources each day (for adults between 19-30 years of age) are:

  • 3.7 liters (about 130 fl oz) for men
  • 2.7 liters (about 95 fl oz) for women.

These dietary reference intakes, however, are based only on survey results of the average amounts that are consumed by people, on the assumption that these amounts must be about right for optimal hydration.

The recommended amounts are of limited value for another reason – total intake figures fail to give a breakdown of how much can be divided up between different kinds of food and beverage.  Consequently, the common sense guidance that is now gaining ground goes along the lines of this summary from the US National Library of Medicine.