Most people know that the human body is largely made up of water. Human body water is the amount of water that makes up over half the human body, on average. This water content can be calculated through several different methods.
In an average adult male, body water constitutes as nearly 60 percent of his weight. A woman's average body water content is 55 percent of her weight, while an infant's water content can be up to 75 percent of his or her weight. This average can vary according to weight, hormonal changes, and other factors.
Water composes much of the body's systems. Blood has a high water volume, with nearly 70 percent of the substance being water. Muscle tissue is nearly all body water, with only 25 percent of the cell groups made up of non-water parts. Bone, body fat, and the brain all contain water as well.
To determine how much water a person needs in his or her system, a simple scale is often calculated. Generally, the higher amount of fat present in the body, the lower the amount of body water will be present. Men who have a percentage of body fat below 15 percent, for example, may have between 60 and 70 percent body water. With a body fat content of 15 to 14 percent, however, the amount of water in the body is less, and may amount to only 49 to 52 percent. Body fat ratios well over 25 percent can account for water levels as low as 37 percent.
Since females contain less water on average than males, but also carry more body fat, their water scale works differently. Women with a fat content of 20 percent or less may contain 58 to 70 percent body water. Those with a fat ratio of 33 percent or higher may, like males, have as little as 37 percent water in their bodies.
These disparities exist due to the water content present in fat. As people lose weight, they are usually advised to consume a greater quantity of water to compensate for the water loss. People who fail to drink enough water to make up water loss may become dehydrated.
Body water exists in three separate categories. Intracellular fluid makes up the most water of the body. This fluid is found within the cell membranes. Intracellular fluid makes up 40 percent of the entire body weight on average.
Extracellular fluid exists outside of the cells. It includes plasma in the blood as well as interstitial fluid that surrounds cells. This fluid accounts for 20 percent of the body's weight. A third category of water, trancellular fluid, makes up a tiny percentage of water in the body. It consists of the small amounts of liquid found in the linings of body organs.