By Abigail Cuffey and Judy Kirkwood
Though you may not need to down a full eight glasses a day, too little water can have negative effects on your body and mood, resulting in more stress. "Once you start to feel thirsty, you're already somewhat dehydrated," says Debra Boardley, PhD, RD, a professor of public health at the University of Toledo College of Medicine. "And we know from research that if you're even mildly dehydrated, you'll feel more tired and drained and less able to concentrate."
A 2001 study found that mild water restriction (no fluids or food from midnight to 11 a.m.) had a negative effect on self-measured alertness. Another found that after just 13 hours without water (think one long, busy day), subjects reported decreased concentration and alertness as well as more headaches.
Your weight and activity level, the air temperature, and humidity all affect fluid needs and some people simply take longer to dehydrate than others. Dr. Boardley says some general tips she's heard include drinking a glass of water with each meal, as well as one glass in between meals and hydrating before and after exercise.