We have been conditioned to believe that eight glasses of water are required each day, but new research published in Science found that daily water needs vary based on numerous factors. Researchers studied 5,604 people aged 8 to 96 from 23 countries, measuring their water turnover—the amount of water lost and replaced each day. They found that for most healthy adults, drinking eight cups of water a day is unnecessary because water needs vary depending on age, sex, body size, physical activity level, athletic status, pregnancy, socioeconomic status and environmental characteristics such as latitude, altitude, air temperature and humidity. People that lived in less developed countries had higher water turnover than people from developed countries. While hydration should be prioritized, most people that pay attention to their bodies and drink when thirsty are likely drinking enough water.