Water sustains life, but until now, figuring out how much water really needs every day has been a guess. Standard recommendations are usually all in one piece – not reflecting the difference in people’s lives, work, and experiences surroundings. A large international study is changing this by showing how daily water is used, depending on climate, activity level, age and factors in which people live. Based on information from thousands of people around the world, these findings provide a clearer and more practical guide to staying hydrated.
Dozens of researchers from around the world, including the National Institute of Health and Nutrition in Japan, the University of Aberdeen, and Duke University in the United States, are led by Professor John Speakman, Dr. Mary Henderson, Dr. Xueying Zhang and Professor Yosuke Yosuke Yosuke Yamada. Their work is in the journal Science.
The team measured how much water the body people used per day by tracking harmless hydrogen in drinking water. This technique, called isotope tracking, uses a special version of hydrogen to follow water as it moves through water. This method allows them to accurately depict the water movement in their bodies in their normal daily life. They found that water demand varies greatly depending on a person’s age, size, activity level, whether he is pregnant and external factors such as temperature, humidity and the economic situation of the country. For example, those who are more active in bodies or live in hot climates will use more water. People in wealthier countries tend to use less water because they can gain more climate control, such as air conditioning, which reduces the loss of sweat.
One of the most surprising findings is the amount of water used varies. Some people only need about one liter a day, while others need more than ten. Young people usually use the highest amount of water, especially men in their twenties and women in their twenties. Professor Speakman explained: “The water renewal means the total amount of water entering and leaving the body every day,” explains. “The largest among men aged 20 to 30, and women aged 20 to 55. “Water demand decreases with age, mainly due to changes in body composition and the situation of active people.
The study also demonstrates the importance of local conditions. “We found a significant curved relationship between outdoor air temperature and moisture renewal,” Professor Yamada said. The curved relationship means that the effect of temperature is not straight, and these two very hot and very cold weather increases how much water people use. People living on mountains or near the equator often need more water. Women who are pregnant or breastfeeding also need more water because of the changes her body is undergoing and produces the water needed for milk.
Based on these findings, the team created two easy-to-use calculations to estimate how much water a person might need per day. These formulas take into account weight, age, physical exercise, humidity, altitude and the level of development in the country. Altitude refers to the height at which someone is above sea level, which may affect the water lost by the body due to breathing. For example, a young athlete living in hot, humid and high altitude areas may need more than twice as much water as his peers living in cooler, low altitude areas, and they are inactive. These tools help provide more tailored water advice than general rules.
The larger information of this study is that water demand is personal. The ancient idea that everyone should drink eight glasses of water every day is inconsistent with the current scientific performance. “A scale is not suitable for drinking water guidelines,” said Professor Speakman, who stressed the importance of updating public recommendations based on real evidence.
This knowledge is more important than ever as the world faces more heat waves, expanding urban areas and growing populations. The study provides a practical way for health experts and governments to plan how much water people need. It also suggests that tracking the water a person uses may provide clues about their overall health, as it is closely related to how active they are and the lean tissue in their bodies. Lean tissue refers to muscles and other parts of the body that are not fat and tend to hold more water.
Journal Reference
Yamada Y., Zhang X., Henderson Met, Sagayama H., Pontzer H., et al. “Differences in human moisture transitions related to environmental and lifestyle factors.” Science, 2022; 378 (6622):909–915. doi:
About the Author
Professor John Stelman He is an internationally recognized expert in physiology and metabolism. He is located at the University of Aberdeen and also affiliated with the Chinese Academy of Sciences, and he spent decades studying energy balance, obesity and human adaptation. His research often uses cutting-edge technologies such as double-labeled water to bridge evolutionary biology and public health to measure real-world energy and water use. Speakman’s work is a prolific scientist with hundreds of publications that help shape a global understanding of how humans use energy and water at different environments, stages of life and activity levels.
Dr. Mary Henderson He is a human biologist and senior researcher specializing in lifestyle, physical exercise and nutrition. Her research, affiliated to the University of Roehampton, London, explores how daily habits and body composition affect overall health. She contributed to large international research on tracking energy and water use, helping to improve public guidelines on moisturizing and health. Henderson’s work draws attention to the various ways people’s environment and behavior affects their health, with the focus on making scientific insights easier to access and act.
Dr. Xueying Zhang is a biomedical researcher working at the intersection of metabolism, environmental health and public nutrition. She is affiliated with Shenzhen Advanced Technology College and Aberdeen University. Her work focuses on large-scale research on human energy use, physical exercise and hydration needs. Zhang has a strong background in data analysis and international collaboration, and in a global effort, Zhang plays a key role in creating more accurate models of human water needs. Her research supports better health policies by showing how personal and environmental factors affect our basic daily needs.
Professor Yosuke Yosuke He is a major researcher at the National Institute of Health and Nutrition in Japan. His work focuses on human physiology, especially body composition, energy consumption and hydration. He uses advanced methods such as stable isotope tracking to understand the amount of water people use and changes over age, lifestyle, and climate. Yamada has been at the heart of creating a global model that helps public health officials develop better guidelines for water and food needs. His contribution is widely respected for its accuracy and practical relevance, in improving our understanding of human health.
