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,
May 18, 2010
Episode #006

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

I bet you’ve heard it said that you need to drink at least eight glasses of water a day in order to stay properly hydrated. Perhaps you’ve also read that by the time you feel thirsty you’re already in an advanced state of dehydration, or that most of us are chronically dehydrated. Chances are also good that you’ve been told that drinking caffeinated beverages like tea and coffee cause you to lose more fluid than you take in.

What would you say if I told you that all of these widely held truths are little more than urban legends?

I can almost hear your shocked expressions! The dehydration myth has become so firmly entrenched in our collective consciousness that it may indeed come as a surprise to learn that there is very little scientific support for any of these notions.

Tales of the Overhydrated

Now, I have to tell you that opera singers are among the most over-hydrated people on the planet. That’s right: My people were carrying water bottles everywhere we went for decades before the rest of you got on the H2O bandwagon. Like most young singers, I was inculcated into the cult of hydration by my first voice teacher, who explained the danger and heartbreak that would follow if I failed to keep my vocal cords adequately lubricated.

I could picture the tragedy: I’d step out on stage, open my mouth to sing, and nothing but a small plume of dust—or perhaps a tumbleweed or two—would come out of my mouth. Hey, the odds of success as an opera singer are slim enough. I certainly wasn’t going to take any unnecessary chances!

So, I joined the legion of singers neurotically sucking down liter after liter every day. It’s a wonder I ever got through the first act of an opera without having to leave the stage four times for bathroom breaks.

Drinking Water Is a Good Habit

Look, as excesses go, drinking a lot of water isn’t a bad one. It won’t make you fat. It won’t rot your teeth or give you a hang-over. Drinking lots of water can temporarily assuage hunger pangs, which dieters find useful. It can also help prevent kidney stones in those susceptible to them. Drinking more can ease constipation and—ironically—also alleviate water retention.

The body has a fairly efficient mechanism for getting rid of excess water so under normal circumstances it’s hard to get yourself into trouble drinking water—except the kind of trouble that happens when you find yourself in bumper-to-bumper traffic on the interstate, or on stage for Act II of Puccini’s Turandot, and the next bathroom break is at least 50 long minutes away. Ouch.

Still, as a nutritionist, I feel compelled to point out that most people can stay perfectly hydrated on significantly less than eight glasses of water a day.

So who started this notion that nothing less than two liters of water a day will keep us from multiple-organ failure? You have to wonder whether this whole thing was somehow cooked up by the $60 billion bottled water industry, which has somehow figured out a way to take a cheap and widely available commodity and sell it at a mark up of anywhere from 250% to 3000%, creating an environmental disaster of nightmarish proportions in the process.

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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)