Most of us know that water is a big deal. In fact, our bodies are largely made of water. No other substance is so important to our physiology or health. Countless metabolic reactions in the human body rely on water as a medium.
Because our bodies are constantly losing water, we need to make sure we replace it. Water loss occurs daily in the stool (200 mL), urine (500 to 1500 mL), sweat, through the skin (500 mL) and respiratory tract (400 mL). These vary with humidity, environmental temperature and respiratory rate. You can see that even if you are not going to the bathroom or sweating, you still lose almost one liter of water through your skin and when you breathe. Conditions such as vomiting, diarrhea or intestinal drainage can further decrease the amount of water in the body.
Dehydration of as little as 1% body weight (2 lb for a 200 lb person) is enough to reduce physical endurance, strength performance, and cognitive performance.
Dehydration can be detected by loss of skin elasticity. If a fold of pinched skin returns to its original shape especially slow, then dehydration is suspected. To do this, pinch the skin on the back of your hand, then see if it stays raised up, or quickly returns to be flat.
So where do we get fluids to maintain balance? Remember that water intake doesn’t come only from drinking water. It also comes from tea, coffee, non-dairy milks, milks, and water from solid foods. With thirst as a guide, humans are generally well hydrated. There is extreme variability in water needs based on climate and physical activity levels. A good rule of thumb:
The amount of water consumed each day (in ounces) should equal 1/2 of your body weight (in pounds)
For men, an average of 16 cups of water a day from fluid and non-fluid sources (e.g. fruits and vegetables) is adequate; for women, an average of 11 cups.
Figure out how much water YOU need to drink every day:
This is how many ounces of water you should drink each day.