What Happens When You Drink a Gallon of Water a Day?

Fluid Dynamics

Nicole Lund, a nutritionist at New York University’s Langone Sports Performance Center, explains the basics of hydration.

How much: “Proper hydration means 85 ounces of water a day from food and beverages, plus more to replenish what you lose when exercising.” (That’s roughly four ounces of water for every quarter-pound of weight lost during your workout.)

Energy and performance: “Physiological changes occur even in the early stages of dehydration, including decreased blood volume and less oxygen delivered to working tissues. These changes make it harder to sweat, which will increase body temperature and heart rate and make you feel more fatigued during exercise.”

Bathroom breaks: Frequent trips to the restroom are normal with increased water intake, Lund says. “As with anything else that you change drastically, your body needs time to adjust if you start drinking a lot more.”

The bottom line: “We all wake up slightly dehydrated. The easiest change you can make is to have a big glass of water first thing in the morning.”