Thirst makes us reach out for water, but even mild dehydration can leave us cranky, confused and fatigued.
Tests by a University of Connecticut (UConn) lab showed that it didn't matter if a person had just walked for 40 minutes or was sitting at rest - the adverse effects from mild dehydration were the same.
Mild dehydration is defined as an approximately 1.5 percent loss in normal water volume in the body, the British Journal of Nutrition reports.
The test results affirm the importance of staying properly hydrated at all times and not just during exercise, extreme heat or exertion, says Lawrence E. Armstrong, study co-author and professor of physiology at UConn's Neag School of Education.
"Our thirst sensation doesn't really appear until we are one (percent) or two percent dehydrated. By then, dehydration is already setting in and starting to impact how our mind and body perform," says Armstrong, an international expert on hydration, according to a UConn statement.
"Dehydration affects all people, and staying properly hydrated is just as important for those who work all day at a computer as it is for marathon runners, who can lose up to eight percent of their body weight as water when they compete," concludes Armstrong.