Hydration 101

Hydration 101 

In our series on nutrition, we spent a lot of time exploring the nutrients in food that give us energy, called macronutrients: carbohydrates, fats, and protein. 

However, there are two other very important classes of nutrients involved in a proper diet. First are micronutrients, aka, vitamins, and minerals – we’ll learn more about these later. 

Here, though, we will investigate the essential nutrient – water. 


Water is so special that it has its own category. While water doesn’t directly “do” anything, such as give the body energy like macronutrients or facilitate metabolic processes like micronutrients, it is crucial to healthy bodily function: 

  • H20 is part of every biochemical reaction in the body. 
  • Needed for digestion, absorption, transportation, dissolving nutrients, elimination of waste products (aka, going to the bathroom), thermoregulation (aka, sweating), and to cushion joints and organs. 
  • Macronutrients like protein, and stored glucose (called glycogen), contain water. 
  • Water fills the space between and inside of cells, and is what makes our blood “fluid.”

As a result, humans are mostly water. In fact, even though you can’t directly “see” it, the human body is made up of 50-80% water. 

Most people have the misconception that if they’re not sweating, they don’t need water. But that’s completely false. Breathing, going to the bathroom, and casual cooling account for half of the water lost in a day (called, “insensible losses“). 

Not including sweating, the human body goes through around 80-100 fluid ounces of water each day (or about 10-12 cups). And activities like exercising or training, especially in the heat, can increase the losses even more. 

There are a lot of downsides to dehydration (or not having enough water in the body), ranging from inconvenient to deadly. Problems include headaches, dry skin, low energy, poor concentration, constipation, decreased athletic performance, and increased pain, to name a few. Dehydration also increases heart rate and affects kidney function. If the water status of the body gets too low, it can lead to death in a few days.

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Where do we get water?

There are many ways to provide water for the human body – it does not (and should not) all come from drinking water directly. Some of our water needs can be met by food (e.g., there’s water in fruits/vegetables as well as most cooked meals, including meats, dairy, and grains). But approximately 80% of our water needs must be met by drinking something fluid.  

In general, water is the best source of hydration. Additional options include sparkling water, decaffeinated tea, and milk. If you’re bored with water, consider adding flavor pick-ups like small splashes of fruit juice or fruit infused water

Caffeinated drinks such as coffee and tea provide fluid, but that fluid leaves the body faster than the options mentioned above – so they don’t hydrate for long. 

Juice, soda, and other sugar-sweetened beverages are tricky. Because while they do indeed hydrate, they also provide a large dose of sugar in the process. 

As we learned in the carbohydrate module, sugar has its purpose in providing a fast burst of fuel. But using a sugar-sweetened beverage for hydrating gives the body more sugar than it knows what to do with (a 12 oz can of Pepsi has 41 grams of sugar or 10 teaspoons. Most organizations recommend no more than 6 teaspoons of sugar per day). These options can play a small, fun role in hydration, but should not be the main option. 

Sports drinks (e.g., Gatorade) and oral rehydration solutions (e.g., Pedialyte) are incredibly valuable tools to prevent and replace large fluid losses from sweating, vomiting, and/or diarrhea. But they are not necessary for day-to-day general hydration as they too come with a decent amount of sugar. But there’s a purpose for sugar in sports drinks – we’ll dive into that in our next segment on hydration!

How much water do we need? 

There are many ways to measure fluid needs, but relying on thirst is NOT at the top of the list. Typically by the time we’re thirsty, we’re already dehydrated. Short of clinical laboratory tests, the most readily available way to gauge your hydration happens in the bathroom. 

The frequency and color of urine is a good personal gauge for hydration. Urine should be a light or pale yellow color. Most bodies urinate 6-10 times a day. The darker the color and lower the frequency, the more likely you are to be dehydrated. Completely clear and frequent urine is a sign to dial down the fluids a bit. If you’re unsure how much is right for you, ask your doctor. 

Please note that IT IS possible to drink too much water. Water is part of a complicated balancing act with a series of vitamins and minerals called electrolytes. Electrolytes help control the water balance of the body and are often lost during the process of sweating. 

When you drink excessive amounts of water without having adequate electrolytes, it can lead to a dangerous, life-threatening health condition called hyponatremia. This does not typically occur when someone is drinking water within reason over the course of the day. But can occur if attempting to drink a large amount of fluid in a relatively short period. 


Water is, in many ways, most of who we are, and it’s essential not only to live but to function at our best. Next, we’ll learn about hydrating for exercise and sports performance, and the role sports drinks like Gatorade play. Check out part 2 of our hydration series here: Sweat Science & Sports Drinks 

Meet The Author: Rebecca Toutant, MA, RDN, LDN, CDE

Rebecca is a registered dietitian, personal trainer, and certified diabetes educator living and working in the Boston area.

Learn more about Rebecca and her background here: Fuel 4 Fitness – Rebecca Toutant

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