How Much Water Do You Really Need to Drink?

A new study suggests that some people may need less than the recommended amount of eight 8 ounces glasses of water daily.

The study from the University of Aberdeen, published in the peer-reviewed journal Science, included 5,604 participants from 26 countries aged from 8 days to 96 years.

Each participant was given a glass of water in which some of the hydrogen molecules had been replaced by a stable isotope of hydrogen called deuterium. It is found in the body and is entirely harmless.

The researchers then estimated water “turnover,” or at what rate the extra deuterium from the glass of water was eliminated from the body.

Intake depends on energy expenditure

The study found that water turnover is higher in hot and humid environments and at high altitudes. Moreover, athletes, pregnant and breastfeeding women, and individuals with high levels of physical activity require a higher water intake.

The most significant factor, however, was energy expenditure, or the amount of energy the body uses to perform essential functions such as breathing or blood circulation.

The research found that in males between the ages of 20 and 35, a group with the highest energy expenditure, the average water turnover was 4.2 liters per day. However, it decreased with increasing age, averaging only 2.5 liters per day in males in their 90s.

Among women, the average water turnover at age 20 to 40 was 3.3 liters a day and also declined to around 2.5 liters by the age of 90.

The study also found that water turnover was higher in developing countries. Researchers think this may be because of the more extensive use of air conditioning and heating that protect individuals from exposure to environmental extremes that elevate water demands.

Study authors note that water turnover is not equal to the requirement for drinking water because 15% of this value reflects surface water exchange and water produced from metabolism. Moreover, a substantial amount of water is provided just by eating.

For a typical person in the US or Europe, probably more than half of the 3.6 liters of water comes from food, which means that the amount needed to be drunk is around 1.5 to 1.8 liters/per day. For example, a woman in her 20s should drink about 1.3 to 1.4 liters per day.

“This study shows that the common suggestion that we should all be drinking eight glasses of water (or around two liters per day) is probably too high for most people in most situations and a ‘one size fits all policy’ for water intake is not supported by these data,” said professor John Speakman from the University of Aberdeen School of Biological Sciences.

Currently, the National Academy of Medicine recommends about thirteen 8-ounce glasses of liquids for healthy men and nine 8-ounce glasses for women.

Why do we need water?

According to the Centers for Disease Control and Prevention (CDC), drinking water is necessary to prevent dehydration. Water is necessary because it helps your body:

  • Keep a normal temperature.
  • Lubricate and cushion joints.
  • Protect your spinal cord and other sensitive tissues.
  • Get rid of wastes through urination, perspiration, and bowel movements.

The color of urine suggests whether a person is adequately hydrated. The darker color, the more concentrated it is, which means it contains less water. However, certain foods, medications, and supplements may change the color of urine.


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