Stop counting cups. There's an ocean of difference in our water needs

A new study of thousands of people shows a wide range in the amount of water they consume around the globe and over their lifespan.

The old eight glasses idea has never been supported by the science because it confused total water turnover with water from beverages and a lot of your water comes from the food you eat. This work is the best we've done so far to measure how much water people actually consume on a daily basis, and how much water comes out of the body.

The new results don't settle on a new guideline. The study, published today in the journal Science, measured the water turnover of more than 5,600 people from 26 countries, and found daily averages on a range between 1 liter per day and 6 liters per day.

Schoeller says there are outliers that turn over as much as 10 liters a day. Pointing to an average doesn't tell you a lot. The big things that correlate with water turnover are shown in the database.

Previous studies of water turnover relied on volunteers to recall and self-report their water and food consumption, or were focused observations of a small group of young, male soldiers working outdoors in desert conditions

The time it took water to move through the bodies of study participants was measured objectively. The study subjects drank a small amount of water. The atoms of a single element have slightly different atomic weights and are distinguishable from other atoms of the same element.

"If you measure the rate a person is eliminating those stable isotopes through their urine over the course of a week, the hydrogen isotope can tell you how much water they're replacing and the oxygen isotope can tell us how many calories they are burning."

More than 90 researchers were involved in the study, which was led by a group that included a former University of Wisconsin–Madison researcher and the section head of the National Institute of Biomedical Innovation, Health and Nutrition in Japan. They compared environmental factors such as temperature, humidity and altitude of participants' hometowns to measure water turnover, energy expenditure, body mass, sex, age and athlete status.

The human development index is a measure of a country that combines life expectancy, education and economic factors.

Men's water turnover volume peaked in their 20's, while women's peaked in their 20's. Newborns replaced about a quarter of the water in their bodies every day.

Men and women are 888-609- 888-609- 888-609- 888-609- A 20-year-old male who is not an athlete is expected to live at sea level in a developed country with a mean air temperature of 50 degrees C. A woman of the same age and activity level with the same amount of weight would go through 2 liters of water.

The researchers found that doubling the energy a person uses will push their water turnover up by about a liter. 0.7 liters of water is added a day. The increase in humidity causes water use to go up. Non-athletes use less than athletes.

hunter-gatherers, mixed farmers, and subsistence agriculturalists had higher water turnover than people in industrialized economies. The more water you go through in a day, the lower your home country's human development index is.

Schoeller says that it's representing the combination of several things. People living in low HDI countries are more likely to live in areas with higher average temperatures, more likely to be doing physical labor, and less likely to be inside during the day. Being less likely to have access to a sip of clean water increases their water turnover.

Schoeller said that the measurement will improve our ability to predict future water needs.

"Look at what's happening in Florida right now, or in Mississippi, where entire regions have been exposed by a calamity to water shortages." The better we know how much they need, the better prepared we are to respond in an emergency.

The researchers believe that the better we can prepare for long-term needs the better.

Population growth and climate change mean that determining how much water humans consume is more important than ever. Water turnover is related to other important indicators of health, such as physical activity and body fat percent.

Variation in human water turnover is related to environmental and lifestyle factors. www.science.org/publish/science.abm8668

Journal information: Science