Are You Dehydrated?

Harriet Hall

Do you worry that you are or might become dehydrated? Do you feel guilty if you don’t drink eight to ten glasses of water a day? Are you tethered to a water bottle? Have you been frightened by warnings on the internet? “Eau” dear! “Water” you thinking? You may have been “flooded” with a tsunami of misinformation. You may be “all wet,” in another sense.

Dehydration can be serious, and it can kill. It warrants special precautions in hot weather and with physical exertion, but alarmist sources have falsely blamed it for various minor symptoms.

It is generally believed that the elderly experience less thirst and have impaired responses to dehydration, and there is experimental evidence to support that belief. But a real-world study found no differences in fluid intake when young and old people were compared.

There are various products on the market that claim to be more hydrating than water alone. You can buy artichoke water, coconut water, watermelon water, and many others. If you become dehydrated, what you need is water, not fancy products with other things added. As Consumer Reports says, “There’s not much truth to the hydration claims.”

Eight to Ten Glasses of Water a Day Is a Myth

My internist thought I was suffering from dehydration and told me to drink more water, but a urinalysis done that same day showed a urine specific gravity of 1.006, at the low end of the normal range, effectively ruling out dehydration. That shows that even doctors have fallen for the myth that we need to drink eight to ten glasses of water a day. Where did that idea come from? As with so many other myths, there is a grain of truth behind it. A very small grain. It was a misinterpretation of a legitimate study.

We constantly lose water through urine, sweat, feces, lungs, etc. Scientists who were studying fluid balance wanted to estimate how much fluid was needed to replace the losses. According to MDLinx, the myth may have originated with “a 1945 publication from the National Research Council’s Food and Nutrition Board that stated that an ‘ordinary standard’ of water for adults is 1 mL for each calorie of food. So, a person who eats 2,000 calories per day would require 2,000 mL of water, or roughly 8 cups. However, the subsequent sentence by the Food and Nutrition Board—’Most of this quantity is contained in prepared foods’—may have been ignored, and so this recommendation was likely misinterpreted as an instruction to drink 8 glasses of water each day.”

The advice is about drinking water, ignoring the fact that there is water in all our foods and beverages. The idea of watermelon water is particularly silly, because watermelon is already 92 percent water. Even coffee helps keep us hydrated. The caffeine has a diuretic effect, but this disappears with habitual use, and the water in the coffee compensates for any fluid loss from diuresis.

Actual water replacement requirements vary with many factors including temperature, humidity, drugs, exercise, vomiting, diarrhea, etc. For most people, assuming no special risk factors, thirst is an adequate guide. Other indicators are urine color and frequency of urination. If you are urinating frequently and your urine is pale yellow rather than deep amber or light brown, dehydration is very unlikely. If you are thirsty and haven’t peed for hours and your urine turns dark, “urine” trouble. You should drink, but not necessarily a glass of water—other beverages will do.

A Silly Mnemonic (Sorry!)

To help you remember, I’ll offer a silly mnemonic. In my experience, the sillier the mnemonic, the more memorable it is. And associations with melodies are particularly effective. When my two daughters got to the age where I thought they should know their address, our address consisted of mostly numbers and was hard to remember. I tried singing the address to the tune of “Happy Birthday” and it worked like a charm: they both learned it very quickly. So, try singing this to the tune of “The Spangled Banner”:

Eau say, can you pee? Is the color still light?

If the answer to both those questions is yes, you are not dehydrated. You can relax, stop worrying, and ditch that water bottle. Trust your thirst to be your guide.

Harriet Hall

Harriet Hall, MD, a retired Air Force physician and flight surgeon, writes and educates about pseudoscientific and so-called alternative medicine. She is a contributing editor and frequent contributor to the Skeptical Inquirer and contributes to the blog Science-Based Medicine. She is author of Women Aren’t Supposed to Fly: Memoirs of a Female Flight Surgeon and coauthor of the 2012 textbook Consumer Health: A Guide to Intelligent Decisions.