How Much Water Should I Drink?

Is the 8-glass-a-day rule an urban legend? Nutrition Diva dives in

Monica Reinagel, M.S.,L.D./N
5-minute read
Episode #6

How Much Water Do You Need to Drink? Nutrition Diva Monical Reinagel

A Drop of Truth in a Sea of Misunderstanding

While I love a good conspiracy theory as much as the next guy, I don’t actually think that’s what happened. Like most urban legends, this one does contain a drop of truth. The average person needs about two liters, or approximately eight glasses, of water a day to replace what is lost through normal biological functions like breathing, sweating, and urinating.

But that doesn’t mean that you need to drink two liters of water. In fact, hypothetically, you don’t have to drink any water at all. For one thing, you can easily get a liter or liter and a half of water just from the food that you eat, especially if you eat lots of fruits and vegetables, which are up to 97% water. (If you’re curious to know how much water you’re actually eating, you can find out by entering a typical day’s intake into the diet tracking tools on NutritionData.com.)

Secondly, contrary to another widely held nutritional myth, coffee, tea, sodas, and other beverages also help fulfill your fluid quota.

What?! Have I lost my mind? Don’t I know that caffeinated beverages like coffee and tea are dehydrating? Actually, they aren’t. Dr. Ann Grandjean is a hydration researcher at the University of Nebraska and she has done some research that might surprise you.

Surprise! Drinking Caffeinated Beverages Won’t Dehydrate You

Dr. Grandjean has demonstrated that if you regularly drink caffeinated beverages, the diuretic effects are almost negligible. In other words, if you drink coffee every day, your body retains the same amount of fluid from a cup of coffee as it does from a cup of water.

If you don’t drink caffeinated beverages regularly, drinking a cup of coffee ends up being the equivalent of drinking about 2/3 of a cup of water. In other words, drinking coffee will hydrate you—just not quite as efficiently as water will.

Hey, don’t get me wrong: I’ve still got a pretty stiff water habit myself and I think you’re better off drinking water than just about anything else. But I’ve seen how overzealous the hydration police can get and thought it was time to separate fact from fiction.

There are a few more important things to say about hydration but they affect a smaller number of folks. So that this episode doesn’t run on too much longer, I’ll just mention them very briefly here but I’ll include some links with the show notes for more information on all of these:

  1. The thirst reflex does decline with age and the elderly are at elevated risk of dehydration.

  2. Excessive thirst and urination can be a warning sign for diabetes.

  3. Those involved in sustained, strenuous exercise or spending extended periods of time in very hot or dry conditions need a lot more fluids to stay adequately hydrated.

  4. When you’re sweating a lot, you need to replace sodium and potassium as well as fluids to prevent a potentially serious condition called hyponatremia.

The Bottom Line on Hydration

But barring ill health, extreme conditions, or intense physical activity, most people will stay well hydrated by eating a reasonably healthy diet and drinking water or other non-alcoholic beverages when they are thirsty. As a rule of thumb, if you are peeing several times a day and your urine is pale in color, you are doing fine.

In a future article I'll explore the potential benefits of coconut water.  In the meantime, if you are uncertain that your drinking water is healthy, please refer to my article on safe drinking water.

For my take on water softeners, head on over here.

These tips are provided for your information and entertainment and are not intended as medical advice. Because everyone is different, please work with your health professional to determine what’s right for you.

Got a burning curiosity about some aspect of nutrition? Need to settle a nutrition-related bet with your roommate or spouse? Nutrition Diva is here for you. Send an email to nutrition@quickanddirtytips.com or leave me a voicemail at 206-203-1438.  I am also on Facebook.

Have a great day and eat something good for me!


An interview with hydration researcher Dr. Ann Grandjean

Dangers of dehydration in elderly

Warning signs of diabetes

Hydration guidelines for Exercise

Avoiding hyponatremia (water intoxication)