Drink eight cups of water a day. We've all heard this widely-touted basic health tip. The origin of the guideline is not known, but is thought to be derived from fluid intake measurements taken decades ago among hospital patients. While the exact amount of water needed each day varies among individuals (and varies day to day based on factors such as weather and exercise), it is still a vital nutrient for optimal health.

Approximately 60% of the body is water. Among all of the vital substances needed by the body, water is second only to oxygen for sustaining life because it is used in every cell. Water helps to regulate body temperature and blood pressure, transport nutrients and other body chemicals, aid digestion, eliminate toxins and waste, lubricate joints and skin, and protect the organs and tissues.

A deficiency of water, known as dehydration, can lead to low blood pressure, clotting of blood, kidney malfunction, and severe constipation.

Water has long been touted as a diet aid, helping overweight people shed pounds, but there has been little research on the topic — until now. Researchers from Virginia Tech University found that participants who drank two 8-ounce cups of water before each meal lost an average of 5 pounds more weight over a 12-week calorie-controlled diet than those who followed the same diet but did not drink the water.

After one year, those who continued to drink water before meals not only kept those pounds off, many also continued to lose about 1.5 pounds more.

"Drinking more water is a pretty simple strategy that may be helpful to people trying to lose weight," said senior author Brenda Davy, associate professor in the department of human nutrition. "We're not saying, 'Drink more water and the body fat will melt away'. But for people who are trying to lose weight and trying to follow a low-cal diet, it's something they can do as part of that."

Weight control likely occurs because the calorie-free liquid can partially fill the stomach, leading to faster satiety. Although the participants followed the same calorie-controlled diet, those who drank water were likely less hungry and less susceptible to cravings and overeating.

Drinking water in place of sugary beverages also helps with weight loss because of the calorie reduction. It is shocking how much liquid calories contribute to weight gain. One regular 12-ounce can of cola contains about 150 calories. If you consume 150 calories a day more than you burn, it could potentially lead to a 15-pound weight gain over the course of a year (150 calories x 365 days divided by 3500 calories).

In general, doctors recommend that adults get about 2000 milliliters (8 to 9 cups) of fluid a day to replace losses that occur through breath, perspiration, urine, and bowel movements. This fluid can come from foods or beverages. (Remember that some foods, such as fruit, are mostly water.) If you are exercising, spending time outdoors in hot weather, or losing fluid through excessive urination or diarrhea, you will need more.

If getting enough water over the course of the day seems like a difficult task, just following the study recommendations of drinking two glasses before each meal will get you at least 6 of the 8 cups you need. If you snack, drink one cup with a mid-morning and mid-afternoon (or evening) snack, and you will easily meet your needs.