Water is a critical nutrient for human survival. Every cell needs water to function. Water comprises about 60 percent of the adult human body; that figure changes to 75 percent in infants and about 55 percent in the elderly. The average adult in the United States consumes about 39 ounces of water per day.
Water is needed to:
- Lubricate joints
- Regulate body temperature via sweating and respiration
- Flush waste from the body
We lose water via:
- Biochemical processes
Body fluid balance is also dependent on nutrients such as potassium, sodium, and magnesium.
Signs of dehydration include:
- Skin stands up on the back of the hand after a gentle pinch test
- Depression of thumb pad remains depressed for several seconds or longer
- Not urinating or very dark yellow urine
- Very dry skin
- Feeling dizzy/fainting
- Rapid heartbeat
- Rapid breathing
- Sunken eyes
- Lack of energy
- Losing more than 10 percent of body weight in water is a medical emergency
How Much Water Does the Human Body Need?
This varies by age, activity level, and climate exposure.
3.7 L per day for men and 2.7 L per day for women to meet the needs of most people (remember, however, that physical exercise and heat stress can greatly increase daily water needs; individual variability between athletes can be substantial).
Estimate fluid needs as body weight in pounds divided by two to get ounces of fluid needed. See example below.
Example: a person who weighs 175 pounds divided by 2 = fluid needs of about 87.5 ounces
(There are eight ounces of fluid in one cup, so this means about 11 cups of fluid per day)
If you are trying to increase your fluid intake and notice you are using the bathroom more, realize this will improve as your body resets to your new fluid intake in about three to five days.