Water makes up roughly 50% to 65% of your total body weight, though the exact number depends on your age, sex, and body composition. A newborn baby is about 75% water, while an older adult may be closer to 50%. For the average adult, the figure most often cited is around 60%.
How Age and Sex Shift the Number
Infants are born with the highest water content of any life stage, around 75% to 78%. By their first birthday, that drops to roughly 65% as body fat increases and proportions change. Through childhood and into adulthood, the percentage continues to gradually decline.
For adults, sex creates a consistent gap. The average adult male’s body is about 60% water, while the average adult female’s is closer to 55%. The reason is straightforward: women typically carry more body fat than men, and fat tissue holds far less water than muscle. Muscle is about 79% water, while fat tissue contains considerably less. So two people of the same weight can have meaningfully different water percentages depending on how much of that weight is muscle versus fat.
In older adults, body water percentage tends to drop further, often falling to 50% or below. This happens because of age-related muscle loss and shifts in body composition. It’s one reason older adults are more vulnerable to dehydration.
Water Content of Individual Organs
Not every part of your body holds the same amount of water. According to data compiled by the U.S. Geological Survey, your lungs are the most water-rich organ at about 83%. The brain and heart are both around 73%. Muscles and kidneys come in at 79%, and skin at 64%. Even your bones, which feel entirely solid, are about 31% water.
These numbers help explain why dehydration affects so many systems at once. When your body’s water supply drops even slightly, organs that depend heavily on water, like the brain and kidneys, are among the first to show the strain. That’s why early dehydration symptoms often include difficulty concentrating, headaches, and darker urine.
What All That Water Actually Does
Water isn’t just filling space. It serves as the transport system for nutrients and oxygen moving into your cells and waste products moving out. It acts as a lubricant in your joints, cushioning the surfaces where bones meet. And it’s your body’s primary cooling mechanism: when you overheat, you sweat, and the evaporation of that water from your skin pulls heat away.
At the cellular level, most of your body’s water sits inside cells (called intracellular water), where it supports protein building, energy production, and cell signaling. The remaining portion sits outside cells, in your blood plasma and in the fluid between tissues, where it maintains blood pressure and delivers nutrients. The balance between water inside and outside your cells is tightly regulated and critical to normal function.
How Much Water You Lose Each Day
Your body cycles through a surprising volume of water every 24 hours. Even at rest in a cool environment, the minimum obligatory water loss adds up to about 1,600 milliliters (roughly 54 ounces) per day. That breaks down to about 800 mL lost through breathing and evaporation from the skin, 500 mL as the minimum urine volume your kidneys need to flush waste, 200 mL in stool, and around 100 mL through minimal sweating.
That 1,600 mL figure is the floor. Physical activity, heat, illness, or high altitude can push daily losses significantly higher. This constant outflow is why you need a steady intake of fluids and water-containing foods to maintain the balance your body works hard to protect.
Why Body Composition Matters More Than Weight
If you’ve ever seen body water percentage on a bathroom scale that claims to measure body composition, it’s using a technique called bioelectrical impedance. The scale sends a tiny electrical current through your body. Because water conducts electricity well and fat does not, the resistance the current meets gives a rough estimate of how much of your body is water versus fat.
These consumer scales are convenient but not especially precise. They can be thrown off by how hydrated you are at the moment, whether you’ve just eaten, and even the temperature of your skin. The clinical gold standard involves drinking a small dose of labeled water (a harmless isotope of hydrogen called deuterium) and then measuring how diluted it becomes in your body fluids over several hours. That tells researchers your total body water volume with high accuracy. It’s not something you’d do at home, but it’s how the reference values used in medicine are established.
For practical purposes, knowing your approximate body water percentage is less important than recognizing the factors that influence it. Carrying more muscle raises it. Carrying more body fat lowers it. Aging lowers it. Staying well hydrated keeps it stable day to day. The 60% figure often quoted as a single answer is really just the middle of a range that shifts with who you are and how your body is built.