How Do You Know When You’re Dehydrated? Measuring Hydration

Your thirst mechanism is not the most accurate way of measuring hydration

By Roberta H. Anding, MS, Baylor College of Medicine and Texas Children’s Hospital
Edited by Kate Findley and proofread by Angela Shoemaker, Wondrium Daily

Can you be dehydrated without feeling thirsty? Professor Anding explains why thirst is not the most accurate indicator of hydration. Here’s a better way to find out if you’re drinking enough water.

Close up of woman drinking water bottle
First thing in the morning, you can determine whether your water intake the day before was sufficient to keep you hydrated. Photo by Monster e / Shutterstock

Hydration and Urine

If you know that eight glasses of water a day may not cover everyone’s needs, how can you determine whether or not you’re hydrated? A significant amount of fluid comes out in your urine—approximately 1.5 liters per day for the average person. Thus, your urine color can help you measure hydration levels.

First-morning urine can provide the most accurate measurement of whether you’re dehydrated. When you get up in the morning, your urine should look like pale lemonade. This indicates that you did a sufficient job hydrating yourself the day before.

There should be some waste products from metabolism that took place overnight, so your morning urine shouldn’t look like water. However, if it looks like apple juice, or you produce a small volume of urine, this means you didn’t drink enough water the day before.

“Now, a question that I always get when we’re assessing that first-morning urine is, ‘What happens if I get up in the middle of the night, two or three times, to go to the bathroom?'” Professor Anding said.

If you see anything dark and concentrated throughout the night—the color of apple juice—then you didn’t do a good enough job drinking the day before.

“The professional athletes that I work with have very high fluid losses, and they have joked with me in the past, ‘Is there something more concentrated than apple juice?'” Professor Anding said. “‘Do we have motor oil, for example, as a color of urine?’ The answer is no. If that’s the case, we probably need to get you to the emergency room.”

Measuring Hydration through Thirst

What about thirst as a measure of hydration? Keep in mind that there’s a lag between the time you get dehydrated and the time you actually experience thirst. Thus, the old adage of, “If you’re thirsty, you’re already dehydrated” probably has some validity to it. 

The other challenge is that the older we get, the less sensitive this thirst mechanism is. For example, you may be visiting a relative in a nursing home, and they’ll say that the only thing they had to drink all day was a cup of tea.

This doesn’t mean that all they needed was a cup of tea. It’s just that they never felt that thirst mechanism.

Other factors can complicate the thirst mechanism as well. Pain medication, for example, will often blunt the sensation of thirst. 

Finally, intentional dehydration that comes along with some medications can complicate thirst. If you’re on a diuretic, you may experience thirst because your physician is trying to clear excess body water to treat heart disease, making it easier for your heart to pump blood.

These examples demonstrate that factors such as medication and age can interfere with how you experience thirst. Therefore, rather than relying on the sensation of thirst as an indication that you need to drink more water, inspecting the color of your urine in the morning is the best way to measure your hydration levels.

This article was edited by Kate Findley, Writer for Wondrium Daily, and proofread by Angela Shoemaker, Proofreader and Copy Editor for Wondrium Daily.

Professor Roberta H. Anding is a registered dietitian and Director of Sports Nutrition and a clinical dietitian at Baylor College of Medicine and Texas Children’s Hospital. She also teaches and lectures in the Baylor College of Medicine’s Department of Pediatrics, Section of Adolescent Medicine and Sports Medicine, and in the Department of Kinesiology at Rice University.