The answer to this question depends on a range of factors, but about 60% of the human body is body water. What’s the rest of your body made up of? A body composition assessment can tell you just that.

Conventional wisdom tells us that we're made up of mostly water. But exactly how much of the human body consists of H2O? If you're an adult, the answer is about 60 percent, but the total changes with age, weight, geography, and other variables. For example, newborn babies have a water weight of about 78 percent, which dips to 70 percent by the time they have their first taste of birthday cake. Starting at puberty, the average man contains a slightly higher water percentage than the average woman. Older adults begin to lose hydration compared to younger adults. In general, a healthy adult's body is composed of at least 50 percent water. 

Factors such as gender, age, and health also influence the amount of water you should drink to maintain an ideal level of hydration. The United States Geological Survey says that men need about 3.2 quarts of water daily, compared to 2.3 quarts for women. Explore how the body's water content affects our wellness and reveals details about disease risk. 

Fun Fact: All our organs are not created equal when it comes to water content, according to data from the Journal of Biological Sciences reported by USGS. The lungs lead the way with approximately 83 percent water content, followed by the kidneys at 79 percent. The brain and the heart are made up of about 73 percent H20. Water composes 64 percent of our skin and 31 percent of our bones. Even our teeth contain about 8 to 10 percent water.

How hydration keeps us healthy

About 66 percent of our body water resides within the cells, known as intracellular fluid, or ICF. Extracellular fluid, or ECF, exists outside the cells. The body uses minerals like sodium and potassium to maintain a healthy balance between ECF and ICF. 

Regardless of its location in the body, H20 is responsible for a number of essential functions (Figure 1). It lubricates joints to give mobility and keep us in motion and provides the saliva that allows us to consume food. When women become pregnant, water makes up a significant portion of the amniotic fluid that cushions and protects the growing fetus. It also shields the spine and other sensitive organs and tissues, helps the body remove waste and maintain a healthy temperature, and transports nutrients throughout the body. Most of all, water builds all our cells and gives them the nourishment they need to survive and thrive.

What does water do for you?

How much is enough H20?

Our hydration needs change by the month, week, day, and even hour depending on our activities, the weather, health status, and weight. We must take in enough water to make up for the moisture we lose through urinating, sweating, and other bodily functions. 

Fun Fact: Did you know the body loses water when we breathe? Our lungs add moisture to inhaled air, and we exhale this water as humidified air.

In a 2018 Nutrients study called Water Intake, Water Balance, and the Elusive Daily Water Requirement, the authors referred to these daily water intake recommendations by age and gender:

• 700 mL for infants 0 to 6 months

• 800 mL for infants 6 to 12 months

• 1.3 L for children 1 to 3 years

• 1.7 L for children 4 to 8 years

• 2.1 L for girls ages 9 to 13

• 2.4 L for boys ages 9 to 13

• 2.3 L for girls ages 14 to 18

• 3.3 L for boys ages 14 to 18

• 2.7 L for adult women

• 3.7 L for adult men

• 3 L for pregnant women

• 3.8 L for lactating women

Healthline suggests estimating your ideal daily water intake in ounces by halving your weight in pounds. In other words, if you weigh 135 lbs., you should strive to drink about 67.5 ounces or 2 liters of H20 each day.

Achieving your hydration goals

You don't have to drink 2 liters of plain water to get adequate hydration—juices, skim milk, and smoothies count, too! Avoid diuretic beverages such as coffee, tea, soda, and alcohol, which cause you to lose water through more frequent urination.

Foods with high water content can also help you stay hydrated. Examples include melons like cantaloupe and watermelon, leafy greens like spinach and lettuce, berries, cucumbers, and citruses such as oranges and grapefruits. 

If you struggle to get enough water throughout the day, try these tested tips:

• Carry a water bottle with you and refill it throughout the day. Choose water over other beverages when possible.

• Drink a full 8-oz glass of water before and after exercising.

• Drink a full glass of water when taking medication.

• Don't wait until you feel thirsty to drink.

The dangers of dehydration

You should familiarize yourself with the signs of dehydration, which include confusion, dizziness, dry mouth, fatigue, urinating less often than normal, and dark-colored urine. Some people have a higher risk of dehydration and associated complications, including pregnant and breastfeeding women, adults ages 65 and older, and individuals who have chronic health conditions such as diabetes and kidney disease. Acute illnesses that cause nausea, vomiting, and diarrhea can also result in dehydration. 

Fun Fact: The color of urine provides one of the best clues to hydration status. Clear, pale yellow, or straw-colored urine indicates a healthy fluid balance. Seek medical attention for dehydration if you notice amber or light-brown urine, especially if you also feel thirsty. 

Seniors should be especially aware of dehydration symptoms, as they may lose their sense of thirst as they age. Thirst is one of the three main mechanisms the body uses to prevent dehydration, along with hormone secretion that signals the kidneys to conserve fluid and osmosis transfer of H2O cells to the areas of the body where they are most needed.

When the body becomes dehydrated, it lacks the electrolytes it needs to perform essential functions. These minerals within body fluids and tissues facilitate water balance, nutrition distribution, acid/base balance, waste removal, and healthy function of the heart, muscles, and nervous system. 

Fun Fact: It's not just a clever name—electrolytes actually carry an electric charge. Examples of these minerals include magnesium, phosphate, chloride, potassium, calcium, and sodium. 

Seek medical care if you notice the signs of dehydration in yourself or a loved one. The health care provider will diagnose and treat the underlying cause of the issue and administer fluids to restore balance in the body.

If left untreated, dehydration can result in blood pressure drops that may cause falls, fainting, or low blood oxygen levels and even a life-threatening health issue called hypovolemic shock. Other complications of severe dehydration include seizures, kidney stones, urinary tract infections, and heat-related events like heat stroke. 

Even with humans’ high body water percentage, it is possible to consume too much fluid. While this condition, called hyponatremia, is rare, it is more likely to affect individuals who have diabetes with uncontrolled blood sugar, kidney disease, or congestive heart failure. 

Fun Fact: Scientists reported on the importance of water balance in the human body way back in 1922. Leonard G. Rowntree at the Mayo Foundation, University of Minnesota, defined the term that year in the journal Physiological Reviews, simply describing it as the sum of the body's fluid intake and output. 

The relationship between water weight and body composition

Fat tissue contains less water than lean mass, so gaining muscle can increase the body's hydration levels. Conversely, people with a higher percentage of body fat have a lower body water percentage. Some body composition tests even measure the test subject while they are on dry land and then when submerged in a water tank to determine percentages of lean muscle and fat. Learning your body composition can provide important information about steps you can take to improve wellness and reduce the risk of disease. 

Using the Watson formula

You can estimate your total body weight (TBW) of water with a calculation called the Watson formula. The formula, which varies by gender, provides a ballpark figure in liters:

• Men: 2.447 – (0.09145 x age) + (0.1074 x height in centimeters) + (0.3362 x weight in kilograms) 

• Women: –2.097 + (0.1069 x height in centimeters) + (0.2466 x weight in kilograms) = total body weight (TBW) in liters

Let's look at an example of a woman who is 164 cm tall (5'5") and weighs 61 kg (about 135 pounds):

-2.097 + (0.1069 x 64)+ (0.2466 x 61) = -2.097 + 6.8416 + 15.0426 = TBW of about 19.97 L, well within the healthy range. From there, dividing TBW by body weight in kilograms provides a body fat percentage—in this case, about 32.74 percent, which indicates some excess fat.  

Exploring Fitnescity options for body composition

You don't have to pull out your calculator to learn more about your body fat, lean mass, and body water percentage. Fitnescity offers safe, accurate body composition tests that wellness-minded individuals can use to set and track progress toward fitness goals. The BOD POD body composition testing system uses air displacement to determine the percentage of fat and lean muscle mass in minutes. The DEXA scan, which uses special X-rays, gives details about the distribution and type of body fat, in addition to the percentage breakdown of fat and muscle. 

Scheduling a body composition scan every few months makes sense, even if you aren't an elite athlete. You can keep a close eye on progress toward goals such as a healthy body fat percentage and easily identify potential health red flags like decreasing muscle mass. Explore the available Fitnescity tests and make an appointment at one of our convenient nationwide locations today for professional, precise DEXA scan and BOD POD testing. 

Sources:

https://www.usgs.gov/special-topic/water-science-school/science/water-you-water-and-human-body

https://www.medicalnewstoday.com/articles/what-percentage-of-the-human-body-is-water 

https://www.healthline.com/health/body-water-percentage 

https://www.discovery.com/science/How-Much-of-Your-Body-Is-Water 

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6315424/ 

https://www.merckmanuals.com/home/hormonal-and-metabolic-disorders/water-balance/about-body-water 

https://journals.physiology.org/doi/abs/10.1152/physrev.1922.2.1.116?journalCode=physrev 

https://medlineplus.gov/ency/article/001187.htm