LAUSR

Water is essential for survival, but one in three individuals worldwide (2.2 billion people) lacks access to safe drinking water. Water intake requirements largely reflect water turnover (WT), the water used by the body each day. We investigated the determinants of human WT in 5604 people from the ages of 8 days to 96 years from 23 countries using isotope-tracking (2H) methods. Age, body size, and composition were significantly associated with WT, as were physical activity, athletic status, pregnancy, socioeconomic status, and environmental characteristics (latitude, altitude, air temperature, and humidity). People who lived in countries with a low human development index (HDI) had higher WT than people in high-HDI countries. On the basis of this extensive dataset, we provide equations to predict human WT in relation to anthropometric, economic, and environmental factors. Description Human water requirements Water requirements for human consumption may become more difficult to manage as changes occur in the Earth’s climate and in human populations. Yamada et al. used an isotope-labeling technique to follow water intake and loss in individuals in a broad range of environments and living conditions. Total water input and output varied according to many factors, including body size, physical activity, air temperature, humidity, and altitude. The authors derived an equation to predict water usage according to such parameters. —LBR A large survey measures human physiological water requirements in varying situations.