Hydration 101: Are you meeting your water needs?

You’ve probably heard the old adage, “Drink 8 glasses of water a day.” You may have heard that water is important to either overall health, or weight loss, or both.

But what’s the real story behind this conventional wisdom? Can we look to real physiology and science to guide our thinking and behavior on hydration?

You bet.

Let’s start with the basics. Why do we even need water in the first place? It’s one of the most essential compounds in the body. Approximately 60% of the human body is composed of water. This means that if you weigh 150 pounds, about 90 pounds of that is water! It plays a role in almost every chemical reaction that occurs in the body. Some key functions are:

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  • Postal Service - Just like the postal service. Water moves nutrients, waste and messages all over your body.

  • Janitorial staff - The kidneys and liver are your main organs that help your body get rid of things that it doesn’t need. You have big filters (your kidneys) and they have a big job. They help regulate blood pressure, hormone regulation, maintain electrolyte balance, excrete and filter waste. Think if a coffee filter… if there is too much coffee and not enough water then it makes more of a sludge (not a appealing idea for your body’s filters). So, water helps keep your kidneys functioning and filtering as they should.

  • Lube shop - The lungs, stomach, intestines, joints, vertebrae - these all have linings or membranes in which water serves as a lubricant or a cushion.

  • Energy central - Remember high school chemistry class? Water plays an essential role in the processes of respiration, digestion (ATP!) and basically everything. Even a slight decrease in hydration exponentially affects the power output capacity of your muscles. Subjectively, you can feel drowsy or fatigued when you’re dehydrated. So grab that glass of cool water instead of the 3pm cup o’ Joe.

  • Thermostat - Blood circulation helps maintain your body’s temperature by bringing or removing warm blood to/from the skin surface. Sweat also causes a condensation effect and cools your body. A change in your hydration status will alter the body’s ability to maintain temperature homeostasis.

But what about weight loss? Will drinking more water make me lose weight?

Maybe. While drinking water along probably won’t cause you to shed excess body fat. Studies have shown that drinking 500mL (about 16 oz, or one pint) of water before a meal is associated with weight loss. Some other studies link water to an increase in metabolism by 24-30%. Perhaps more importantly, drinking a few gulps of water prior to a meal probably helps to improve hunger and satiety.

Given the importance of water in all of the chemical reactions that occur in your body, it also makes good logical sense that if you are chronically dehydrated, the body will be more concerned with maintain essential functions and survival than losing weight.

How much water do you really need? The old rule of thumb, 8 glasses of water per day, at approximately 8 ounces per glass, only provides 64 ounces of water, or 1,893mL, per day. More up-to-date science tells us this isn’t enough.

While everyone is different, the average baseline water needs are 25 - 35 mL per kilogram, per day.


Baseline H20 Needs = 35mL x body weight in kilograms

(To determine your weight in kilograms, simply divide your weight in pounds by 2.2).


So, if you weigh 150 pounds, or approximately 68 kilograms, then you need at a baseline between 1,700 - 2,380mL of water each day.

If you perform any type of exercise, then we recommend at least an additional 1,000mL of water, or more if you sweat a lot.

So, there’s a good chance that drinking eight 8-oz glasses of water per day is not enough.

What’s your water goal?

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Use the equation above to determine your baseline water needs. Factor in your daily exercise habits, and determine your “water goal.” Do you meet that every day? What steps can you put in place to make it easy to meet your goal? Some tips:

  • Carry a water bottle with your everywhere. Find out the size of your water bottle, and determine how many times you need to fill and drink it per day. Most standard sizes are 16 oz (500mL), 24 oz (700mL), or 32oz (1000mL)

  • Give your water a subtle flavor with cut up lemons, limes, oranges, grapefruit, or cucumber

  • Drink 16 oz before each meal to potentially improve metabolism and satiety

Do other beverages count towards the water goal?

We’re going to say NO. While other fluids can contribute to your hydration status, we want to build the habit for hydrating ourselves with delicious, refreshing, regular old water. This is because many of our clients who struggle with weight loss have an unhealthy dependence on sugar- or artificially flavored beverages, and have a hard time drinking regular water.

Is more always better?

Not necessarily. If you’re meeting or slightly exceeding your water goal, there are probably few benefits to drinking more. At best, you’ll simply excrete the extra water as urine. At worst, you could disrupt your body’s homeostatic balance by altering its pH or osmotic gradients. So, do some quick math, and stick to the goal.

But what about electrolytes?

Exercise and endurance hydration will be a topic of another post. However, our general rule of thumb is that unless you’re training as an endurance athlete with multiple 75+ minute training sessions per week, you probably don’t need to worry too much about supplementing your water with electrolytes or consuming any type of sports drinks. Our food has plenty of salt and nutrients to replace what is lost in sweat for most moderately active people. There are some exceptions (such as when you’re sick with with fluids coming out of one.. Or *ehem* two ends), but in general, stick to water.

So, what’s your water goal? Spend the next week or two trying to meet your hydration goal daily, and take note of how you feel. Stay tuned for additional posts on caloric beverages and exercise hydration!


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