Central Texas runners , other athletes and just about everybody you meet outdoors nowadays carries a water bottle - mainly to make sure they get the recommended eight glasses a day, or about 1.5 liters. But that's a general guideline. Most medical experts recommend you get that much fluid, but not necessarily just water. Many people interpret that to mean extra water in addition to other fluids from food, soft drinks, coffee, tea or juices.

Recently, a couple of researchers published a study in the Journal of the American Society of Nephrology that questioned assumed health benefits of drinking a lot of extra water.

Dan Negoianu and Stanley Goldfarb at the University of Pennsylvania reviewed published clinical studies devoted the topic and concluded there is no evidence that most people need to increase their water consumption, except during exercise or high heat and humidity. Especially if the purpose is one of the major and long held beliefs: That extra water improves kidney function and cleans more toxins out of the body, that it helps control weight gain, that it improves skin tone or that it prevents headaches.

They did find solid evidence that people who live and work in hot, dry climates or athletes have increased water needs. Their findings were consistent with other research that indicates thirst is actually a very good indicator of the need for hydration.

Why You Need Water

The human body is composed of about 60 percent water. The average person loses about 10 cups of fluid a day through perspiration, urination and other bodily functions. To be healthy and not dehydrated, that fluid must be replaced.

However, experts estimate we get somewhere around four cups of fluid through the food we eat. The rest generally comes from fluid consumption and, more than likely, if you drink when you are thirsty, you will be meeting your body's daily needs.

Obviously, there are factors that significantly influence whether you need to be drinking more such as exercise, environment, illness and pregnancy. You sweat more during exercise or in hot and humid weather. If you have fever or experience diarrhea or vomiting, you need extra fluids. If you are pregnant or nursing, your body needs the extra fluids to support your child's needs both before and after birth.

Strike a Balance

Remember the studies done by Negoianu and Goldfarb consider the fluid needs of the average person for normal activities. If you are one of the many Central Texans who train for or participate in area races, especially long runs, you should get extra hydration to replenish the fluid you sweat away as your body attempts to cool itself. You need to stay hydrated to prevent heat-related illnesses, especially when you're exercising outdoors and the temperature climbs above 80 F.

But there is no need to over load the body with fluids. Otherwise, the extra water may dilute the body's balance of sodium in the blood and lead to hyponatremia, a condition that results from too few electrolytes in the blood that can cause convulsions. It led to the death of a runner in a recent Boston Marathon. Hyponatremia can be worse that dehydration because it is more difficult to detect. Most cases of dehydration can be reversed with fluids.

Seton Northwest Clinical Dietitian Janessa Slatky recently recommended a reasonable hydration schedule for a marathon and the basic advice still applies to heavy exercise or racing, especially when it's hot.

"When you are running, it's a good idea to drink before you get thirsty so you don't run the risk of getting dehydrated, just not too much," says Janessa. "Drink a little before you begin, then replenish with a few ounces along the way every couple of miles."

Janessa recommends the following guidelines for fluid intake to help you stay hydrated and perform your best.

• Daily ...8-10 cups to avoid thirst
• 2 to 3 hours before activity ..1 1/2 to 2 1/2 cups
• 5-10 minutes prior to exercise ...1/2 to 1 cup as possible
• Every 15-20 minutes during exercise ..3/4 to 1 1/2 cups (3-6 gulps)
• After activity ...at least 2-3 cups within 30 minutes

"Take a peek at your urine. The lighter your urine output color (think lemonade ) the more hydrated you are. The darker your urine output color (think apple juice ) the more likely you are dehydrated and need to drink more fluids. Water is the most important nutrient for active people and is a fine choice for most workouts. However, during continuous workouts lasting 90 minutes or longer, your body may benefit from a sports drink."

Janessa, a regular runner herself has completed a marathon.