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How much water do I need? Plus, other H20 facts

Okay, really, how much water do we need? The Mayo Clinic says there's no one-size-fits-all answer for this because of differences in exercise, environment, overall health and factors like pregnancy or breast-feeding. The National Academies of Sciences, Engineering, and Medicine says a rough estimate is about 15.5 cups of fluids for men and about 11.5 cups of fluids a day for women, but what you eat also contributes to your fluid needs. (Fruit is almost all water, for example.)

• The Mayo Clinic suggests drinking a glass of water or other calorie-free beverage with each meal and between each meal, as well as before, during and after exercise, and when you're feeling hungry. (Thirst is often confused with hunger.)

• Almost 300 million Americans, the vast majority, get their tap water from public water systems. The Environmental Protection Agency requires monitoring for more than 80 drinking water contaminants, which are included in annual water quality reports if they are detected. The other 15 percent of Americans receive water from private water systems that do not have governmental oversight. Owners of private wells are responsible for ensuring that their well water is safe from contaminants.

• Worldwide, 768 million people lack access to improved drinking water supplies and 2.5 billion people, half of the developing world, lack access to adequate sanitation.

• Most tap water contains fluoride, a salt compound that helps prevent cavities, something that has on occasion been controversial. (Pinellas County chose not to fluoridate its water for a year.) The Centers for Disease Control and Prevention declared drinking water fluoridation one of the top 10 public health achievements of the 20th century. The U.S. Public Health Service now recommends an optimal fluoride concentration of 0.7 milligrams per liter, enough to prevent tooth decay but not enough to have any other deleterious health effects.

• Americans drink more than a billion glasses of tap water per day and use 127 percent more water today than in 1950.

• Only 1 percent of all the world's water can be used for drinking. Nearly 97 percent of the world's water is salty or otherwise undrinkable, and the other 2 percent is locked away in ice caps and glaciers.

• Being hydrated can boost brain function by 14 percent, according to a study by the University of East London. (After all, 80 percent of your brain tissue is made of water.) Dehydration can also have a negative impact on our mood and energy level, according to researchers at the University of Connecticut's Human Performance Laboratory. Being hydrated also speeds up metabolism and reduces the appearance of fine lines and wrinkles.

Sources:; the Mayo Clinic; the Centers for Disease Control and Prevention; the National Academies of Sciences, Engineering, and Medicine

Laura Reiley, Times food critic