Next to oxygen, water is the human body's most important nutrient. Yet 75 percent of Americans are chronically dehydrated and fail to drink the eight, 8-ounce servings of water per day recommended by health and nutrition experts.

Here are the facts on why it's important to ensure you're properly hydrated.

• Water plays a vital role in regulating body temperature, transporting nutrients and oxygen to cells, removing waste, cushioning joints and protecting organs and tissues.

• Water's ability to dissolve a multitude of substances allows our cells to utilize valuable nutrients, minerals and chemicals in biological processes, and water's surface tension enables our body to mobilize these elements efficiently.

• Up to 60 percent of the human body is water, the brain is 75 percent water, blood is 82 percent water, and lungs are nearly 90 percent water. 

• The body loses water via the skin by perspiration, kidneys by urine, lungs by exhaled water vapor, and intestine by feces.

• At normal activity levels, people lose two to three cups of water a day in perspiration. But during an hour of vigorous exercise, people sweat out approximately a quart of water.

• Deep yellow or amber colored urine can be a sign of dehydration.

With all that in mind, here are five tips for maintaining proper hydration :

• Don't wait until you're thirsty to drink water. By the time you feel thirsty, you probably have already lost two or more cups of your total body water.

• Don't substitute caffeinated coffees, teas, sodas or alcoholic beverages for water. Caffeine and alcohol can act as diuretics, causing you to lose wate through increased urination.

• Don't underestimate the amount of fluids lost from perspiration. You need to drink two cups of water for each pound lost following a workout.

• Start and end your day with a serving of water. Your body loses water while you sleep.

• When it's warm outside, cold water is the best fluid for keeping hydrated. Cool water is absorbed much more quickly than warm fluids and may have a positive effect on cooling off your overheated body.

Barbara Levine, R.D., Ph.D., is Director of the Nutrition Information Center at the New York Hospital-Weill Medical College of Cornell University.