Fiction: You Must Drink 8 Glasses of Water Daily

There really is a good reason to be skeptical about any health claim that relies on some stringent guideline for the entire human species. Case in point, there really is no good reason why you should be drinking eight glasses of water every day, as you have undoubtedly have heard numerous times from multiple unreliable sources. In fact, the entire meme may have arisen from a misunderstanding:

In 1945 the Food and Nutrition Board, now part of the National Academy of Sciences's Institute of Medicine, suggested that a person consume one milliliter of water (about one fifth of a teaspoon) for each calorie of food. The math is pretty simple: A daily diet of around 1,900 calories would dictate the consumption of 1,900 milliliters of water, an amount remarkably close to 64 ounces. But many dieticians and other people failed to notice a critical point: namely, that much of the daily need for water could be met by the water content found in food.

Furthermore:

The Board revisited the question of water consumption in 2004. Its panel on "dietary preference intakes for electrolytes and water" noted that women who appear adequately hydrated consume about 91 ounces (2.7 liters) of water a day and men about 125 ounces (3.7 liters). These seemingly large quantities come from a variety of sources—including coffee, tea, milk, soda, juice, fruits, vegetables and other foods. Instead of recommending how much extra water a person should drink to maintain health, the panel simply concluded that "the vast majority of healthy people adequately meet their daily hydration needs by letting thirst be their guide."

As the most interesting man in the world says, "stay thirsty my friends"—just don't take that too literally.