People who drink enough water to be adequately hydrated are half as likely to be obese as people who are inadequately hydrated. That’s the verdict of researchers at the University of Michigan Medical School, who assessed water intake as adequate or inadequate based on urine samples of more than 9,500 people. Nearly one third were found to be inadequately hydrated. HealthDay reports that the researchers can’t prove cause and effect, and they don’t really know why water drinkers are thinner. One researcher suggests that obese people eat rather than drink when they are thirsty. Another thinks drinking water may make people feel fuller, so big water drinkers eat less. They also note that there’s a very easy way to tell if you are under-hydrated: if your urine is dark yellow, you need more water. So, how much water should we be drinking? The Institute of Medicine suggests 125 ounces of water daily for men and 91 ounces for women, from all food and beverages combined.