In spite of what many so-called health sites and some news outlets proclaim, it isn't necessary to drink eight glasses of water each day to be healthy, as explained in the New York Times. This myth just keeps on popping up especially in the summer when we are warned of the dangers of dehydration. While it's true that dehydration is a possibility for those engaging in vigorous exercise, especially in a hot, dry environment, for most of us it's a non-issue.
As we've noted in the past, the whole idea that we need eight glasses of water per day may have come from an old recommendation that we need about eight glasses of fluid per day. And much of that fluid could just as easily come from foods with high water content, such as most fruits and vegetables (a tomato, for example, is over 95 percent water). Various scientists have reviewed the literature, but have found no basis for the eight-glasses-of-water recommendation.
Indeed, too much water consumption can actually be harmful, and if taken to the extreme, even deadly. Drinking too much too quickly can result in a dilution of the blood and a condition known as hyponatremia a too-low concentration of sodium in the blood which in turn can be fatal. Some cases of fatal over-hydration have been described in military literature, specifically with troops who have over-consumed water while engaging in strenuous training exercises.
Dr. Ruth Kava, ACSH senior nutrition fellow, notes that "any liquid beverage caffeinated or not is a useful source of fluid, as are most foods, except those that have been dehydrated. A person's thirst is a reasonable guide as to when to drink, and how much."