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The Facts Behind H2O

The Facts Behind H2O
14 February 2000 --

While individual fluid needs vary depending on body weight, climate and activity levels, most physiologists/nutritionists agree that people need to drink at least eight eight-ounce glasses of fluid daily, equivalent to two litres. That equals a drink each hour of the working day.

Why is it important to drink so much?

  • On average an adult's body is made up of 10-12 gallons of water (up to three-quarters of our body weight). Good hydration is vital to health. Without water, we would die in a matter of days, whereas we can survive for up to eight weeks without eating food.
  • We lose about one to two litres of fluid each day when we breathe, sweat, urinate, and defecate. We lose even more when we are physically active. This fluid has to be replaced.
  • Every part of the body, from the individual cell to the entire circulation system, depends upon water to function.
  • Our kidneys filter out impurities from the bloodstream and excrete them via urine. Kidneys need an adequate amount of fluid (minimum one litre) to function properly.
  • Infants, children, pregnant women and elderly people have special needs for fluids.

What are the signs of dehydration?

The effects of dehydration range from thirst and weakness to impaired kidney function. In extreme cases, dehydration can even lead to coma and death.

Signs of dehydration


  • Thirst
  • Headache
  • Fatigue
  • Flushed skin
  • Dry mouth and throat


  • Rapid heart rate
  • Dizziness
  • Low blood pressure
  • Weakness and lack of energy
  • Highly concentrated urine, but low in volume


  • Muscle spasms
  • Swollen tongue
  • Poor blood circulation
  • Increased weakness
  • Failing kidney function

Note: Re-hydration is complete when urine is clear.

How can dehydration be avoided?

  • Drink plenty of fluids! In addition to water, there are lots of options for fluid replacement, from milk and fruit juice to soft drinks and soups.
  • Fruit and vegetables can also be a source of fluids as they can contain up to 95 percent water.

Do people need to drink more fluids when exercising?

  • People who are physically active should drink additional fluids over and above the recommended two-litre daily minimum as appropriate.
  • There is a time lag between water loss and thirst. It is important for athletes to ensure that they consume fluids two hours before exercising and replace lost fluid during and straight after training and competition.
  • Is it possible to overdose on fluids? Most people have little risk of drinking too much fluid. Experts estimate that the healthy human body can cope with an intake of up to 20 litres (about five gallons) of fluid per day!

Five good reasons to drink plenty of fluids

  1. Fluid is essential in helping your body rid itself of impurities.
  2. Fluid is essential for sweating, the body's natural cooling system, even more important in hot, humid weather or when exercising.
  3. Proper hydration aids good digestion.
  4. Fluid intake helps keep skin moist and supple.
  5. Proper hydration helps prevent fatigue.

Reprinted with permission from the Asian Food Information Centre (AFIC). AFIC is a non-profit organisation with the aim of communicating science-based information on a broad range of nutrition and food safety issues. Based in Singapore, AFIC covers the entire Asian region except for Japan and Korea. AFIC can be reached at Tel: +65 832 7637 and Fax: +65 464 9260.

Date reviewed: 14 February 2000

This website and article is not a substitute for independent professional advice. Nothing contained in this website is intended to be used as medical advice and it is not intended to be used to diagnose, treat, cure or prevent any disease, nor should it be used for therapeutic purposes or as a substitute for your own health professional's advice.  All Health and any associated parties do not accept any liability for any injury, loss or damage incurred by use of or reliance on the information.


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