We’re told to drink at least two litres of water a day to remain healthy. And for good reason—most of our bodies are made of water, and without it, our temperature would shoot upwards, our joints would go unlubricated, and our organs would quickly break down, among other things.
So water is crucial for our survival. Humans are made up of roughly 60% water1, which can vary dramatically from 45% to 78% depending on our age, sex, body fat percentage, and hydration levels.
Let’s break these down, starting with sex.
Water Percentage for Males and Females
Body water percentage differs slightly for men and women. Men are about 60% water, and women about 55%. This is due to the differences in body fat between men and women. Men tend to have more lean muscle and women more fatty tissue, and because fat contains less water than muscle, women tend to have a lower water percentage in their bodies.
A higher body water percentage can lead to higher energy, increased strength, and a more effective immune system. That’s why resistance training is great for both men and women.
Water Percentage by Body Fat
As mentioned above, lean muscle holds more water than fat, so the more muscular you are, the higher your body’s water percentage will be. This is one of many reasons why going to the gym and strengthening your muscles is so good for you.
Water Percentage by Age
Babies tend to have a water percentage of around 65% (although this can reach as high as 78%). This allows them to maintain their fluid equilibrium more effectively. By the time we reach a year, our water percentage hits the adult average of around 60%.
Elderly people end up being around roughly 50% water, which can dip as low as 45%. Again, the reason for this is muscle mass—we lose muscle as we age, and so we also hold less water in our bodies.
Water Percentage by Hydration Level
Obvious as it sounds, the more water you drink, the higher your body water percentage will be. If you lose between 2 to 3% of your body water, you’ll start to feel thirsty and will probably reach for the water jug.
What you eat makes a difference too. Salty and sugary foods are fine in moderation, but they will reduce your body’s water percentage, especially if you don’t drink enough water.
Water Percentage by Sex and Age
- 12 to 18 years – 59%
- 19 to 50 years – 59%
- Over 51 years 56%
- 12 to 18 years: 56%
- 19 to 50 years: 50%
- Over 51 years: 47%
Where is Water Stored in the Body?
About two-thirds of the body’s water is stored inside the cells (intracellular fluid), and the rest is stored outside the cells (extracellular fluid). The water outside includes the space between cells (also called “interstitial” fluid), as well as your blood plasma, which is a whopping 90% water.
Water percentage varies by organ too. Here’s a breakdown of water percentage by body part:
- Lungs: 83%
- Brain: 80%
- Heart: 75 to 80%
- Kidneys: 79%
- Muscles: 70 to 75%
- Liver: 70 to 75%
- Skin: 64%
- Blood: 50%
- Bones: 31%
How is Body Water Percentage Measured?
The amount of water in your body is called your total body water, and can be measured through methods such as dilution, hydrometry, or something called the Watson Formula.
- Ohashi, Yashushi, Ken Sakai, Hiroki Hase, and Nobuhiko Joki, 2018, “DRY WEIGHT TARGETING: THE ART AND SCIENCE OF CONVENTIONAL HEMODIALYSIS.” Seminars in Dialysis