Do you really need to drink 8 glasses of water per day? (Hydration series part 1 of 3)

Hydration is a source of confusion for many. It doesn’t help that the recommendation to drink 8 glasses of water per day is so broad it’s barely accurate. People’s need for fluid intake is EXTREMELY variable. It depends on your body size, the water in the foods you eat, your activity level, and the temperature of your environment, nowater-38154_640t to mention other factors like pregnancy or disease.

In fact, the old “8 glasses of water per day” adage was not born from any scientific evidence at all (there is a fascinating research study in which scientists tried very very hard to uncover what evidence the recommendation even came from. They couldn’t find any).

Nutritionists do still loosely use this recommendation so people will understand the importance of fluid intake generally. However, there’s a few things you should know:

1) Per the recommendation, a “cup” or “glass” is 8 ounces. That is a very small glass to most of us. For those of you not familiar with ounces, a small coffee at Starbucks (and most other coffee shops) is 12 ounces.

2) fluid does not need to be only water. All fluids hydrate you because they’re mostly water!

3) The recommendation makes it seem like more is always better and it’s not possible to drink too much water. First of all, drinking a ton of unnecessary water causes you to have to pee a lot, what a pain! Also, although very rare (and difficult to do), you can drink too much water, dilute your cells of sodium and die. This is why every year kids die during water drinking competitions. This can also occur in marathoners who drink only water, which I will discuss next week.

People also may not realize that food can be a good source of water intake. Fruits and vegetables tend to be high in water and can be very hydrating. On the other hand, if you’re someone who takes in a lot of fiber (from grains) you may require a bit more fluid intake.

My feeling is that water intake is overemphasized by well-meaning health/fitness/nutrition enthusiasts who do not know the science behind hydration (I once saw Jillian Michaels on TV telling people to drink TONS of water daily to “flush out” lactic acid…lactic acid does not cause soreness and is a beneficial byproduct of exercise!!!). My hope is that, for some of you who have tried forcing yourself to drink more and more water, or felt bad about not drinking as much as you’ve heard you’re supposed to, this information is relieving!

Next week, in part 2 of this 3-part series, I’ll discuss whether it’s true that “you’re already dehydrated once you’re thirsty,” as people say, and I’ll give you three crucial steps to take to ensure you’re hydrated. And in part 3 of this series I’ll be explaining what firefighters and active people should do to stay hydrated.

Have you been victim of the more-water-is-always-better campaign? Does this info totally surprise or not sit well with you? Ask me questions below!


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By | 2018-06-01T07:33:11+00:00 February 5th, 2014|Uncategorized|3 Comments

About the Author:

Dr. Karlie Moore has a PhD in Exercise Science and Nutrition and specializes in firefighter health. She has conducted fitness testing on hundreds of firefighters and has created the most comprehensive online wellness program for fire departments called the FitCulture program. Dr. Moore is also married to a firefighter and so understands their lifestyle and the health challenges associated with it.


  1. Sadie February 5, 2014 at 4:20 pm

    Hey Karlie! In #2 you said the fluid does not only need to be water. I’m one that struggles with eight glasses of simply water a day, however I drink a lot of liquids. My drink du jour is coffee. (White wine too, but I digress…:-) I’ve heard coffee dehydrates. What is the rule for coffee?


    • Karlie February 5, 2014 at 8:19 pm

      Hi Sadie, the idea that coffee dehydrates you comes from the notion that it’s a diuretic. But it’s only so if your body isn’t use to coffee, so that doesn’t apply to habitual coffee drinkers. Nutritionists I think are hesitant to promote coffee as a hydrating food because excess caffeine does have negative health effects so we don’t want people getting all their fluids from coffee. But if you’ve ever made a pot of coffee then you know it’s mostly water!

  2. […] Do you really need to drink 8 glasses of water per day? (Hydration series part 1 of 3) […]

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