But most people don't realize how easily they can become dehydrated. Lethargy, headaches, and fatigue are common. Put on heavy winter clothes and take a brisk walk in Milwaukee, and you lose water through sweat just as you would on a beach. The dehydration effects are just the same. Winter also brings flu season, which can be dangerous because fevers can quickly dehydrate the body.
Diarrhea also causes increased fluid loss.
Kleiner cautions that these recommended amounts assume very limited physical activity. What is really important to understand is that the USA suffers from chronic low-level dehydration. A number of studies show that Americans are running on empty by not taking in the required amounts of fluid. We drag a little, our minds aren't quite 'into it,' and we begin to make little mistakes. According to most experts, dehydration contributes to stone formation.