Most people know that the human body is mostly made up of water. Human body water is the amount of water that makes up more than half of the human body, on average. This water content can be calculated through several different methods.
In an average adult male, body water makes up nearly 60 percent of his weight. The average body water content of a woman is 55 percent of her weight, while a baby's water content can be up to 75 percent of her weight. This average can vary based on weight, hormonal changes, and other factors.
Water makes up much of the body's systems. Blood has a high volume of water, and nearly 70 percent of the substance is water. Muscle tissue is almost all of the body's water, with only 25 percent of the cell groups made up of non-water parts. Bones, body fat, and the brain also contain water.
To determine how much water a person needs in their system, a simple scale is often calculated. In general, the greater the amount of fat present in the body, the less body water is present. Men who have a body fat percentage of less than 15 percent, for example, may have between 60 and 70 percent body water. However, with a body fat content of 15 to 14 percent, the amount of water in the body is less and can be as low as 49 to 52 percent. Body fat ratios above 25 percent can represent water levels as low as 37 percent.
Since women contain less water on average than men, but also have more body fat, their water scale works differently. Women with a fat content of 20 percent or less can contain 58 to 70 percent body water. Those with a body fat ratio of 33 percent or more may, like men, have as little as 37 percent water in their bodies.
These disparities exist due to the water content present in the fat. As people lose weight, they are generally advised to consume more water to compensate for the water loss. People who don't drink enough water to make up for water loss can become dehydrated.
Body water exists in three separate categories. Intracellular fluid makes up the largest amount of water in the body. This fluid is found within cell membranes. Intracellular fluid accounts for 40 percent of total body weight on average.
Extracellular fluid exists outside of cells. It includes plasma in the blood as well as the interstitial fluid that surrounds cells. This fluid represents 20 percent of the body's weight. A third category of water, transcellular fluid, makes up a small percentage of water in the body. It is made up of small amounts of fluid found in the linings of the body's organs.