The human body is roughly 60% water by weight in the average adult, though the exact number depends on your age, sex, and body composition. That single figure masks a wide range: healthy adults can fall anywhere from about 40% to 73% water, and the percentage shifts meaningfully across your lifetime.
Average Water Percentage by Age and Sex
Men carry more water than women at every age, primarily because they tend to have more muscle mass (muscle is about 76% water, while fat tissue holds considerably less). For adults between 19 and 50, men average around 59% water while women average about 50%. After age 50, both numbers drop: men average roughly 56% and women about 47%.
The trend is even more dramatic at the extremes of life. Newborns are about 75% water by weight. By the time an infant reaches their first birthday, that figure settles to around 60%, and it gradually approaches adult levels by age 12. In older adults, total body mass and water content both decline, which is one reason dehydration becomes a bigger risk with aging.
Why the Range Is So Wide
If you look at the full range for adult men aged 19 to 50, it spans from 43% to 73%. That’s not measurement error. It reflects real differences in body composition. Muscle tissue is roughly 76% water, while fat tissue stores far less. A lean, muscular person will have a higher body water percentage than someone with more body fat, even if they weigh the same. This is also the main reason for the gap between men and women: on average, women carry a higher proportion of body fat.
Hydration status, recent food intake, and even time of day also shift the number. After a meal high in sodium or carbohydrates, your body retains more water temporarily. Intense exercise can cause short-term water loss through sweat, then a rebound as you rehydrate. These fluctuations are normal and can move your body weight by a few pounds in either direction over the course of a single day.
Water Content of Individual Organs
The 60% figure is a whole-body average, but individual organs vary enormously. The lungs are the most water-rich major organ at about 83%. The brain and heart are each roughly 73% water. Muscles and kidneys come in at around 79%, and skin sits at about 64%. Even bones, which feel completely solid, are 31% water.
Blood fits the pattern: it’s about 80% water overall. The liquid portion of blood, called plasma, is 90% water. Plasma makes up a little more than half of your blood volume, with red and white blood cells and platelets accounting for the rest.
What All That Water Actually Does
Water isn’t just filling space. It’s the solvent your body uses to transport nutrients, oxygen, and hormones to cells. It carries waste products to your kidneys and liver for filtering. It cushions your brain and spinal cord, lubricates your joints, and forms the basis of saliva and digestive fluids. Your body also relies on water for temperature regulation: when you overheat, blood vessels near the skin dilate and sweat evaporates, both of which depend on adequate water supply.
Because water is involved in so many processes, even small deficits have measurable effects. Losing just 1% to 2% of your body weight in water (that’s roughly 1.5 to 3 pounds for a 150-pound person) is enough to impair attention, memory, and motor skills. You’ll typically feel thirsty before reaching that point, but not always, especially during exercise or in hot weather.
How Body Water Is Measured
If you’ve ever stepped on a “smart” bathroom scale that reports body water percentage, it’s using a technique called bioelectrical impedance. The scale sends a tiny electrical current through your body and measures how quickly it travels. Water conducts electricity well, so more resistance suggests less water (and more fat). These readings are convenient but imprecise. They shift based on your hydration, when you last ate, and even whether your feet are wet.
The gold standard in research settings is isotope dilution. You drink a small amount of water tagged with a traceable form of hydrogen or oxygen, wait for it to distribute evenly throughout your body, then provide a blood or urine sample. By measuring how much the labeled water was diluted, researchers can calculate your total body water with high accuracy. This method is too cumbersome for everyday use, but it’s how the reference values you see in medical literature were established.
Keeping Your Body Water in a Healthy Range
Your body is constantly losing water through breathing, sweating, and urination, and it replaces that water through drinking, eating, and normal metabolism. Most healthy adults maintain their water balance automatically by responding to thirst, though older adults sometimes lose the sensitivity of that signal. Foods contribute more than people realize: fruits, vegetables, soups, and even cooked grains all deliver meaningful amounts of water.
There’s no single ideal body water percentage to aim for, because the healthy range depends so heavily on your age, sex, and muscle-to-fat ratio. What matters more is staying consistently hydrated. Urine color is a practical, low-tech gauge: pale yellow generally indicates adequate hydration, while dark yellow or amber suggests you need more fluid.