No, the human body is not 98% water. While water is a major component, the actual percentage ranges from about 50% to 75%, depending on age, sex, and body composition.
Where the 98% myth comes from
The idea that the human body is 98% water likely stems from a misunderstanding of molecular counts. Water molecules are small and abundant, so by sheer number, they make up a large fraction of all molecules in the body. But when measuring by mass—which is how body composition is clinically assessed—the percentage is far lower. This confusion between molecular count and weight leads to exaggerated claims that don’t reflect physical reality.
Actual water content by age and body type
Water levels vary significantly throughout life and between individuals. Newborns are about 75% to 78% water, which explains their soft, pliable bodies. As people age, total body water decreases, especially in older adults, where it can drop below 50%. This decline is partly due to reduced muscle mass, which holds more water than fat. Since fat tissue is only about 10% water, people with higher body fat have lower overall water percentages.
How water is distributed in the body
Water isn’t evenly spread. About two-thirds of the body’s water is inside cells, known as intracellular fluid. The remaining third is outside cells, including interstitial fluid and blood plasma. Even blood, often thought of as mostly water, is only about 90% water, the rest is made up of cells, proteins, and minerals. Organs like the brain and heart are around 73% water, but denser tissues like bone bring the whole-body average down.
Why bone and fat matter
Bone is a major contributor to the body’s solid structure and contains only about 31% water. The mineralized matrix of calcium and collagen gives bones strength and rigidity. Fat tissue, on the other hand, is hydrophobic and holds very little water. Because of this, two people of the same weight can have vastly different water percentages based on muscle and fat distribution. A lean athlete may be over 65% water, while someone with more body fat may be closer to 50%.
Comparisons with other species
Some animals, like jellyfish, truly are 95% or more water. They rely on their aquatic environment for support. Humans, in contrast, have evolved to live on land with a rigid skeleton and dense tissues that require less water. Even plants like cucumbers and lettuce are over 90% water, but they use cell walls for structure. Humans rely on bones and connective tissue, which displace water and reduce the overall percentage.