THE IDEA that humans should drink a minimum amount of water for optimal health dates back centuries. In the 19th century, hydropathy claimed water could cure various ailments. Vincent Priessnitz, an Austrian farmer, promoted this idea, eventually earning the title “father of hydrotherapy.”
In 1945, the U.S. Food and Nutrition Board recommended people drink 2.5 litres of fluid daily, but the entire statement clarified that most of this comes from food. Over time, this detail was forgotten, leading to the idea that all fluids must come from drinking water.
Later, nutritionist Fredrick J. Stare, PhD, recommended drinking at least six glasses of water daily, admitting that the number was not scientifically based.
Debunking the 8×8 Rule
The 8×8 rule—eight glasses of eight ounces daily—has become common wisdom, but is it necessary? In 2002, Heinz Valtin, MD, published an article in the American Journal of Physiology, finding no scientific evidence supporting the rule. Studies show people remain hydrated from food and other drinks, not just water.
How to Hydrate Properly
Many people chug a water bottle when thirsty, but experts say this isn’t the best way to hydrate.
“It’s best to sip a little throughout the day,” says Lindsay Baker, PhD, senior scientist at the Gatorade Sports Science Institute. Large amounts at once are quickly eliminated through urine, offering little hydration benefit.
Evan C. Johnson, PhD, explains that chugging water triggers a bolus response, which flushes excess fluid rather than storing it. Instead, he suggests drinking small amounts consistently to avoid alerting the body to an excessive intake.
Hydration from Food
Fluid doesn’t just come from drinking water—many foods contain significant water. Soups, fruits, yoghurt, and vegetables contribute to daily hydration.
“People who eat water-rich foods naturally get more hydration,” says Joseph G. Verbalis, MD, professor of medicine at Georgetown University.
Are Coffee and Beer Dehydrating?
A common belief is that coffee and alcohol dehydrate you, but research shows otherwise.
“You can drink a beer and lose a little, but not enough to affect hydration,” says Tamara Hew-Butler, PhD, associate professor at Wayne State University.
Baker agrees: “All beverages count.” While caffeinated drinks may slightly increase urination, they still contribute to hydration.
The Rare Risk of Overhydration
While dehydration is common, overhydration is rare. Drinking excessive water in a short period can cause hyponatremia, dangerously diluting sodium levels in the blood.
In 2007, a California radio contest led to a woman’s death from water intoxication after drinking two gallons in three hours.
How Much Water Do You Need?
Fluid needs vary based on activity level, environment, and diet. Athletes require more water and electrolytes, while sedentary individuals may need less.
Listening to thirst is the best guide—drink when you’re thirsty, and sip water throughout the day rather than forcing a set amount.
The Bottom Line
The 8×8 rule isn’t harmful but also unnecessary for healthy adults, especially in midlife and beyond. Hydration comes from various sources, including food, water, and other beverages. The best approach? Drink when you’re thirsty, and don’t overthink it.
