In a study published in Frontiers in Human Neuroscience, thirsty people had significantly faster reaction times after drinking just 500 mL or 2 cups of water than that of those who had drank nothing at all. People who did not consider themselves thirsty, however, had about the same reaction times with or without a drink. More surprisingly, both thirsty and not thirsty individuals seemed to adapt to new problems slower with water than they did without it. Vasopressin, the hormone that activates the thirst response, is also linked to attention and arousal, explains Caroline Edmonds, PhD, a psychologist at the University of East London. Thirst may be distracting while completing simple tasks like acknowledging something and reacting quickly, but for more thought-stimulating activities that involve trial and error, it may actually serve to boost your attentiveness and focus to be thirsty.  “It’s that type of rule-learning task and being able to change your behavior on the basis of evidence on what you’re seeing in the environment—that was worse when people had had a drink,” says Dr. Edmonds.  Water is still by far one of the healthiest beverages you can put in your system, but it’s important to remember that too much of anything can be bad for you and, more importantly, that everything is relative. Don’t need it? Don’t drink it. But if you’re craving that quenching H2O sensation, then by all means, pour yourself a glass. More from Prevention: Bored With Plain Water?