Even if you're not yet thirsty, a lack of water may be affecting your disposition, energy level, and ability to concentrate, according to a new study.

PROBLEM: Most people only drink water when they're thirsty. But what if even just mild dehydration, defined as approximately 1.5 percent loss in normal water volume, can already cause our minds and bodies to underperform?

METHODOLOGY: Researchers at the University of Connecticut's Human Performance Laboratory recruited 25 young, healthy women who exercised for less than an hour a day. The participants were hydrated the night before each of the three evaluations where they were tasked to walk on a treadmill to induce dehydration. They were also put through a battery of cognitive experiments that measured vigilance, concentration, reaction time, learning, memory, and reasoning. Their scores were then compared against a separate series of tests when the individuals were not dehydrated.

RESULTS: Lack of water caused headaches, fatigue, and difficulty in concentrating. The women also perceived the cognitive tasks as more difficult when slightly dehydrated, even though there was no significant reduction in their ability to think. Another study involving men showed similar adverse effects.