Experts Revisit the Eight-Glass Water Rule

Daily fluid needs are not identical for everyone. U.S. guidelines suggest 92 ounces, or 11.5 cups, for women and 124 ounces, or 15.5 cups, for men. Those totals include food as well as drinks, with food supplying about one-fifth of daily fluids. The familiar eight-glass idea is less exact: eight 8-ounce glasses equal 64 ounces, while larger glasses change the total. It can still serve as a starting point for someone who is not drinking enough.

Hydration needs may shift with sweating, exercise, surroundings, age, body size, diet, pregnancy or breastfeeding, alcohol, and medical conditions. Water is the preferred choice, though very low-calorie drinks such as herbal tea can also contribute; excessive caffeine may raise dehydration risk. Foods including cucumbers, watermelon, asparagus, celery, strawberries, and zucchini also contain fluid. Electrolyte drinks may be useful after heavy sweating, but should not be the only beverage.

Fluids support digestion, skin, kidney function, temperature control, nutrient transport, waste removal, joint and spinal lubrication, and brain function. Adults can monitor hydration partly by urine color: dark orange or darker yellow may signal a need for more water, although bright yellow can be normal with multivitamins or B vitamins. Drinking too much also carries danger. Hyponatremia occurs when blood sodium falls below 135 milliequivalents per liter and can impair tissues, especially the brain, with possible coma, lasting brain damage, or death.