innerbody

Last Updated: October 03, 2017

Water: It's More Than Just a Drink

Overview

Eight glasses of water a day, right? Maybe not. For some time now, experts have told us to drink eight 8-ounce glasses of water each day. Because we’ve heard this mantra for so long, it’s difficult to imagine that it wouldn’t be the truth. There isn’t any evidence for it, however, concluded scientific reviews in 20021 and 2008.2 What’s more, in 2004 the Institute for Medicine (IOM) issued new fluid guidelines stating that average healthy Americans should let thirst be their guide and that even caffeinated beverages like cola, tea and coffee count toward our fluid requirements.

On This Page

  1. Water in the Body
  2. Water in the Diet
  3. Water and Electrolytes: A Critical Balance
  4. Maintain Safe Hydration Levels

That’s not to say that water is not important. In fact, at least 50% of your body is water. Take a look at what it does for you.

Water in the Body

Male athlete drinking from a water bottle

Water has the following functions within the human body.

Even though the myth of drinking eight glasses of water a day may not be true, water is still an essential ingredient in your body’s system.

Water in the Diet

If you are the typical American adult, you consume about 20 to 25% of your daily water from solid foods. Fruits, vegetables, cooked grains and even meats and cheese provide water. The rest of your water intake comes from beverages of all types.
 

Red apple

Water Content of Selected Foods and Beverages (food and its percentage of water by weight):

Source: USDA Nutrient Data Lab3

How much fluid do you really need?

The IOM report does not specify water requirements. Rather it includes guidelines for total fluid intake. From both food and beverages, women should consume, on average, 91 ounces of total water, and men should have 125 ounces of total water daily. This should cover your fluid losses in urine and feces, and the normal, but continual losses from the lungs and skin. The water loss from the skin and the respiratory tract is referred to as insensible water loss. If you are sick, you may lose additional water from nasal secretions, through vomiting or diarrhea or from sweating with a fever. Thus, you’ll need to drink additional beverages.

How should you measure your fluid intake?

There is usually no reason to measure your water intake or impose a water requirement on yourself. Healthy people will meet their fluid needs by paying attention to their thirst. If you have heard and believed that thirst is a poor indicator of hydration status, you have fallen prey to another myth. Though we often hear such things as, “by the time you’re thirsty, you are already dehydrated,” the truth is that experts define dehydration when the concentration of blood has increased by at least 5%, but thirst begins much sooner than that, usually before the concentration of blood rises 2%. Thirst may not indicate hydration status, however, for individuals with medical conditions requiring fluid control, individuals taking some medications, athletes or those involved in other strenuous activities, or people living in especially hot climates.

What are some liquid sources of water?

Three soda bottles nestled in ice

Athletes and heavy sweaters may benefit from sports drinks. They are ideal for individuals who are very active for at least 60 minutes. They contain fluid and electrolytes lost in sweat, as well as carbohydrates to refuel and prevent fatigue. For casual exercisers who sweat little, sports drinks likely offer little more than water and extra calories. Added vitamins in sports drinks are unnecessary because we do not lose vitamins in sweat. Sodas, sweet tea and fancy coffee drinks also provide you with necessary water, but they give you plenty of unnecessary added sugars and calories, so have them only rarely.

To keep your body hydrated, you can do more than just drink water. Many healthy foods contain water, as well as some of the other liquids you consume, such as milk. Eat and drink a variety of foods and liquids to make sure your fluid intake is where it should be.

Water and Electrolytes: A Critical Balance

Electrolytes are substances that, when dissolved in water, dissociate into positively and negatively charged ions. This makes them capable of carrying an electrical current. For example, when you dissolve salt (sodium chloride) in water, sodium and chloride separate. Sodium provides a positive charge and chloride brings a negative charge. Electrolytes help maintain fluid balance because they draw water to them. Through osmosis, water will cross cell membranes to make the concentration of dissolved particles the same on both sides. The major electrolytes are sodium, potassium, chloride and phosphorus.

Sodium

Salt shaker on its side, with salt spilled out

This is the major positively charged electrolyte in the extracellular fluid (fluid outside the cells).

Potassium

An appetizing pile of clams in their shells

This is the major positively charged electrolyte in the intracellular fluid (fluid within the cells).

Chloride

This is the major negatively charged electrolyte in the body.

Phosphorus

Three brown eggs

This is the major negatively charged electrolyte in the intracellular fluid, usually combined with oxygen in the body to form phosphate.

Electrolytes are no less important than fluid for maintaining proper hydration status. And as you can see, each of the above minerals plays multiple roles in the body - from bone density to immune function, muscle contraction and nerve transmission. Eating a balanced diet with an abundance of fresh fruits and vegetables will help assure the proper intake of these minerals.

Maintain Safe Hydration Levels

You can see how intricately tied water and electrolytes are in the body. A problem with one easily leads to a problem with the other. It might be hard to imagine that water, something so pure, so critical for life can be toxic.

Water is an essential part of the human body. Make sure you drink enough fluids and eat foods that contain water. You may not be able to measure the exact amount of ounces you consume during a day, but if you eat healthy foods, and drink fluids that contain more water than sugars or additional calories, you should maintain safe hydration levels.

Next Nutrition Guide:

WHAT DETERMINES WHAT WE EAT

Sources

  1. Valtin Heinz. “Drink at least eight glasses of water a day.” Really? Is there scientific evidence for “8 x 8”? Am J Physiol Regul Integr Comp Physiol 283: R993-R1004, 2002.

  2. Kolso J, Jeckel K, Wildman EC. Water, Hydration and Health: What Dietetics Practitioners Need to Know. SCAN’s Pulse Winter 2012 Vol.31, No. 1.

  3. USDA Nutrient Data Lab http://ndb.nal.usda.gov/index.html  Accessed March 9, 2012.

  4. http://www.cdc.gov/Features/dsSodium/

  5. Dietary Guidelines for Americans, 2010. U.S. Department of Agricultural, U.S. Department of Health and Human Services, 2010Pg 22

  6. Fulgoni VL III, Keast DR, Bailey RL, Dwyer J. Foods, fortificants, and supplements: where do Americans get their nutrients? J Nutr 2011;141:1847-54.

Related Topics

Authored by: Jill Weisenberger, MS, RD, CDE