It depends!
Water truly is life – we can go without eating for weeks and survive but get very sick if we do not get adequate water for a few days.
You are doubtless familiar with “rules” such as the need to drink 8 glasses of water a day. The problem with relying on such simple rules is that the real answer truly is “it depends.”
A man who is 6-foot-5 and weighs 205 pounds needs more water than a woman who is 5-4 and weighs 110.
It is currently sunny and pushing 90 degrees F. Walking up to get the mail left me sweating. We clearly need more water under these conditions than we do when it is 65 and shady.
People doing physical work outdoors in the heat need more water than those sitting at desks in air-conditioned offices.
“Water” includes most other liquids such as herbal tea and fruit juice – but not caffeinated drinks or alcohol, which tend to pull water out of the body.
Finally, and perhaps less obvious, we do not get water only by drinking. Many foods, particularly fruits and vegetables, contain significant amounts of water. Our habitual diet will change the amount of water we need.
Then how do you know how much water to drink? A simple, reliable way to assess this is to look at your urine. If your urine is dilute – clear to pale yellow in color – you are adequately hydrated. If your urine is closer to apple juice than lemonade in color, you are dehydrated and need to drink more.
If your urine is very dark, you ought to seek medical attention, as you may need intravenous fluids.
Do not depend on thirst as your sole indicator. If you are thirsty, you are probably somewhat dehydrated, but lack of thirst is not as reliable as the color of your urine.
So: drink up!
Edward Hoffer MD is Associate Professor of Medicine, part-time, at Harvard.
What Does The Doctor Say?
By Dr. Edward Hoffer