When you find yourself struggling to concentrate on something, try having a glass of water. That’s the conclusion of a new, detailed analysis of more than 30 studies into the effects of dehydration,reports. The researchers, from the Georgia Institute of Technology, found that going thirsty had no significant impact on reaction times and other basic cognitive functions. But for more complex tasks that require focused attention or coordination, dehydration did appear to impair people’s performance. Examples include “maintaining focus in a long meeting, driving a car, [or] a monotonous job in a hot factory,” said study leader Mindy Millard-Stafford. “Higher-order functions like doing math or applying logic also dropped off.” Millard-Stafford and her colleagues found that cognitive impairment tended to begin when people lost 2 percent of the water in their body. For the average person, that equates to about 35 fluid ounces of sweat—roughly what you’d produce with an hour of moderate hiking.