We always hear about the importance of staying well hydrated and the fact that water makes up over half of our bodies by weight, but what is a good body water percentage?
How much of your body weight is water? What is the average body water percentage for men and for women? Does body water percentage change with age?
In this guide, we will discuss the functions of water in the body, the average body water percentage by age and sex, a good body water percentage, and how to improve your hydration status to increase your body water percentage.
Let’s dive in!
What Is Body Water Percentage?
With certain biometrics, which is a term that just refers to different measurements of internal or external characteristics of your body, the meaning of the biometric is relatively well understood.
For example, we all inherently understand body weight when you step on a scale or body temperature when you use a thermometer to measure your temperature.
Body water percentage can be a bit more confusing.
Most of us have heard that the body is composed primarily of water, and this is essentially what body water percentage is describing or measuring.
Your body water percentage is a measure of the percentage of your total body mass that is composed of water, not your body volume.
In other words, when you step on a scale and obtain a body weight, your body water percentage would tell you how much of that total body weight is made of fluids rather than solid tissues such as minerals, proteins, cell structures, etc.
So, where does body water come from?
You might think that your body water percentage is just your blood volume, but actually, while blood is mostly composed of fluid (which is known as blood plasma), there are also cells in the blood.
In addition to the plasma or fluid portion of blood, any body fluid contributes to your total body water percentage. This includes lymph, synovial fluid in joint capsules, and interstitial fluid (the fluid in cells), among others.
According to the USGS, all organs and tissues are composed of some water, even bone.1The Water in You: Water and the Human Body | U.S. Geological Survey. (n.d.). Www.usgs.gov. https://www.usgs.gov/special-topics/water-science-school/science/water-you-water-and-human-body?qt-science_center_objects=0#qt-science_center_objects The following table shows the percentage of water in different organs and tissues:
|Organ or Tissue
|Brain and heart
|Muscles and kidneys
What Is A Good Body Water Percentage for Adults?
“On average, a healthy body water percentage for an adult is around 50-65% of your total body weight,” explains Dr. Barber.
Dr. Barber says that there are several factors that can impact average body water percentage, which is why there is a range for “normal or good body water percentages.”
Here are some of the main factors that influence an individual’s percent body water:
“Body water percentage tends to be higher in younger individuals (up to 75%) and gradually decreases with age,” says Dr. Barber. “This is due to changes in body composition and a decrease in muscle mass as people get older.”
Men tend to have a slightly higher body water percentage compared to women.
According to Dr. Barber. “This difference is primarily because men typically have more muscle mass, which contains more water while women tend to have more fatty tissue on average, which contains less water.”
Studies suggest body water percentage increases during pregnancy and decreases postpartum.
As can likely be surmised, your own body water percentage can fluctuate on a day-to-day basis.
These fluctuations within an individual rather than between two individuals are mostly based on hydration status.
Dehydration leads to a lower body water percentage while being well-hydrated increases it.
We often hear about the importance of staying well-hydrated during exercise. Of course, staying well hydrated is important at all times because all of the cells in your body need water.
However, it is particularly important during exercise because when you lose fluids through sweat, your blood plasma volume drops.
Blood carries oxygen and your muscle cells need that oxygen to produce energy to sustain your physical activity.
As a result, when you are exercising in a dehydrated state and you have a lower blood plasma volume, there is less blood in your circulatory system, and your heart has to be faster in order to maintain the same cardiac output.
Cardiac output (Q) refers to the total volume of blood pumped by your heart in a minute.
It is the product of the number of times your heart beats in a minute (your heart rate, or HR) multiplied by how much blood is being pumped with every beat, which is known as stroke volume (SV).
Thus, the equation for cardiac output is Q = HR x SV.
All of this is to say that studies have found that dehydration of just 1 to 2% of your body weight can decrease exercise performance.2Goulet, E. D. B. (2013). Effect of exercise-induced dehydration on endurance performance: evaluating the impact of exercise protocols on outcomes using a meta-analytic procedure. British Journal of Sports Medicine, 47(11), 679–686. https://doi.org/10.1136/bjsports-2012-090958
This is not a loss of body fat, but rather of body water.
If you lose 1 to 2% of your total body weight from body water, the decrease in your body water percentage is even more significant since only about 50 to 65% of your body is water.
Let’s say that you weigh 180 pounds, and your normal body water percentage before beginning your workout is 55%.
This means that 99 pounds of your total body weight is made up of fluids.
If you lose 2% of your body weight through dehydration, you have lost 3.6 pounds of fluid.
Instead of 3.6 pounds of fluid being just 2% of your body water percentage, 3.6 is actually 6.5% of your water weight (99 pounds).
Now, instead of having a healthy body water percentage of 55%, your body water percentage has dropped to under 48.5%.
This might be an unhealthy low body water percentage, depending on your age and sex.
Note that some salts are also lost in sweat, so it’s not an exact mathematical equation here, but sweat is 99% water, so the overall takeaway is that being dehydrated or your hydration status, in general, can have a significant impact on your average body water percentage.
Why Is Body Water Percentage Important?
Dr. Barber says, “The amount of body water in your body is important for maintaining overall health and proper bodily functions.”
She provides numerous reasons why maintaining optimal hydration status and a good body water percentage is so essential for good health:
Why Stay Well-Hydrated?
- Hydration: All of the cells in the body need water
- Temperature Regulation: “Body water helps regulate your body temperature. It acts as a coolant, helping to dissipate heat when you’re hot (through sweating), and helps conserve heat when you’re cold,” says Dr. Barber.
- Digestion and Nutrient Transport: Water plays a role in the digestion of food, and the absorption and transport of nutrients throughout your body, as well as the excretion of waste.
- Circulation: Blood is primarily composed of water, and sufficient body water is necessary for blood volume and circulation.
- Detoxification and Elimination: Water helps the body remove waste and toxins through urine, sweat, and bowel movements.
- Joint Lubrication: Dr. Barber says that adequate hydration helps maintain the lubrication and cushioning of joints, reducing the risk of joint pain and injury.
How Do You Measure Your Body Water Percentage?
Although we have all sorts of wearables and fitness trackers these days that can provide biometrics like your heart rate, heart rate variability, and even skin temperature, measuring your body water percentage isn’t as straightforward.
There are several different ways that you can measure your body water percentage, so the accuracy of these methods varies as does their accessibility.
The gold standard method for body water measurement is the Deuterium Dilution method.
“It requires the administration of an isotope into the body by ingestion or intravenously and the collection of a blood, saliva, or urine sample after a period of equilibration,” explains Dr. Barber.
“This method is time-consuming and a big drawback is the ingestion of an isotope.”
DEXA scans and bioelectrical impedance can also assess body water percentage and lab tests like urine-specific gravity can provide insight into your hydration levels.
Some body fat scales provide an estimate of body water percentage and there are now some wearable hydration monitoring devices such as the Nix Biosensor.
You can also use the Watson formula to estimate body water percentage:3Watson, P. E., Watson, I. D., & Batt, R. D. (1980). Total body water volumes for adult males and females estimated from simple anthropometric measurements. The American Journal of Clinical Nutrition, 33(1), 27–39. https://doi.org/10.1093/ajcn/33.1.27
- Watson formula for men: 2.447 – (0.09145 x age) + (0.1074 x height in centimeters) + (0.3362 x weight in kilograms) = total body water (TBW) in liters
- Watson formula for women: –2.097 + (0.1069 x height in centimeters) + (0.2466 x weight in kilograms) = total body weight (TBW) in liters
If you need some motivation to drink more water, check out our 14-day drinking water weight loss challenge here.
- 1The Water in You: Water and the Human Body | U.S. Geological Survey. (n.d.). Www.usgs.gov. https://www.usgs.gov/special-topics/water-science-school/science/water-you-water-and-human-body?qt-science_center_objects=0#qt-science_center_objects
- 2Goulet, E. D. B. (2013). Effect of exercise-induced dehydration on endurance performance: evaluating the impact of exercise protocols on outcomes using a meta-analytic procedure. British Journal of Sports Medicine, 47(11), 679–686. https://doi.org/10.1136/bjsports-2012-090958
- 3Watson, P. E., Watson, I. D., & Batt, R. D. (1980). Total body water volumes for adult males and females estimated from simple anthropometric measurements. The American Journal of Clinical Nutrition, 33(1), 27–39. https://doi.org/10.1093/ajcn/33.1.27