Quick, what’s the capital of Poland? The square root of 36? If you can’t come up with the answers, don’t worry — you might just be thirsty.

A new report shows that when you drink water, your brain works better.

“Lots of studies have shown that dehydration is linked to poor performance on memory and attention tasks,” says Caroline Edmonds, PhD, University of East London senior psychology lecturer. Some research has shown, for example, that the fluid-filled spaces in the brain become enlarged when someone is dehydrated, which causes brain tissue to shrink and makes it harder to think. Thirst can be maddeningly distracting, too. When it’s gone, the brain is free to focus on more important things.

To test water’s brain-boosting power, Edmonds asked 34 thirsty men and women to perform a series of mental tasks, measuring their reaction time, memory, and learning capabilities. Half were given water; the other half weren’t. The subjects who guzzled about 2 cups of water before completing the tasks increased their reaction time by 14 percent. In addition, the water drinkers felt happier, less confused, and more relaxed.