Because it has no calories, you might not think water would be an essential element in nutrition and in reducing the risk of heart attack, but it is a highly important aspect of health. Among its many functions, water keeps our kidneys functioning efficiently. When the kidneys cannot do their job properly, the liver must take on some of that task and if this happens it cannot metabolize fat into energy as well. Water also aids in digestion, carries nutrients, aids in building tissue, transports waste from the body and helps maintain the body's normal temperature.

About 60% of a person's weight is made up of water. A fluid loss of as little as 2% of body weight can affect physical performance. A 5% loss can cause stomach and muscle cramps. Heat stroke, which can be fatal, often occurs at 7% to 10% fluid loss. Although there are large amounts of water in vegetables and fruit, which is helpful to vegetarians, anyone who consumes high levels of fiber should be sure to consume sufficient water.

Contrary to what many people think, a good way to combat excess fluid retention is to drink water. When the body doesn't get enough water, it conserves all the moisture it can. The extracellular spaces it is stored in (swollen feet, hands and legs) hoard the water until the threat of dehydration is no longer sensed. The best way to tell your body to release the stored fluids is to give it water. Salt can cause higher water retention, requiring extra water to dilute it. Lowering salt intake is easy to do and extra amounts of water will flush the sodium from the system.

Thirst is not always a good indication of the need for water. In many people, the sensation of thirst doesn't occur until the body is already dangerously dehydrated. The best way to assure a proper fluid balance for an average size person is to drink at least 6 to 8 eight ounce glasses of water a day. Heavier people need to drink even more water. A half-hour heavy workout can produce as much as three quarts of sweat, a 4% fluid loss for a 150 pound person. That loss needs to be replaced. Beyond the basic 6 to 8 cups of water a day, for each 100 pounds of body weight, an additional 8 ounce cup of water should be taken for each hour of light exercise, 12 ounces (1 cups) for moderate exercise and 20 ounces (2 cups) of water for each hour of strenuous activity.

Plain cool (not iced) water is the best way of replacing fluid loss. Fruit juice, mixed half and half with water, or sports drinks with not more than 10% carbohydrate concentration are also good. High-carbohydrate sports drinks (more than 24 grams of carbohydrate per eight ounces) are not advised. Sodas, undiluted fruit juices and high-carbohydrate drinks actually slow down absorption and do not allow immediate fluid replacement.

In exercise that lasts up to 1 hour, taking small sips of water or low-carbohydrate sports drinks is often helpful, but it is better to avoid drinking large amounts while exercising. For marathons and long exercise sessions, larger quantities of fluids are needed. For longer events, a good test is to weigh yourself before and after. For each pound of weight loss, you should drink 16 ounces (2 cups) of water.

Some drinks, such as coffee and tea, can increase fluid loss because they have a diuretic effect. Alcohol is a stronger diuretic; the body needs eight ounces of water to replace the loss from just one ounce of pure alcohol. Hot weather and low humidity can add to the dehydration effect. Almost all foods contain water, but they also may contain carbohydrates, protein and fiber, which increases the need for water. Vegetables range from 70% to 90% water and can be used as a part of the 6 to 8 cups of water needed daily.

If you decide to suddenly increase your water intake, you may find that it will take two or three weeks for your system to become accustomed to the change. You'll likely make more frequent trips to the bathroom for a week or two, but your bladder will gradually become used to handling the increased flow, and your routine will soon return to normal.

Water is not a substitute for foods, but it can help you avoid the temptation of high calorie or high fat offerings, especially when you're away from home. A large glass of water just before you are tempted may help you control your craving.