Water, water, everywhere, but are you hydrated?  
Many people believe that since swimmers exercise in water, they don’t sweat. In a word, WRONG!  Even immersed in the pool, water loss can be significant. For every 1000 meters of swimming (1100 yards) swimmers will lose 4-6 ounces of water through sweating. This equals almost two pounds of water weight loss for a 6000 meter workout. 
Don’t believe it? Try weighing yourself before and after practice. One pound of weight loss is equal to 16 ounces, or one pint of water. 
Why is this so bad? Your body is made of a great number of things, but 40-70% of your body is water! In the blood it transports energy to working muscles and carries away waste products. Water in urine eliminates waste products, and water in the form of sweat allows the body to lose heat and keep cool. Water is therefore essential to athletic performance both in and out of the pool. Too little water leads to dehydration with symptoms like headache and fatigue. Good hydration is essential for a good race or practice.
 What about fluid replacement drinks such as Gatorade and PowerAde? Research shows that water is ideal for workouts lasting less than an hour. For longer workouts where you burn more energy, the glucose (form of sugar) in the sport drinks may keep muscles from becoming energy depleted. The sweet taste of a sports drink may encourage swimmers to drink more. Though small amounts of glucose and sodium (salt) do not have a huge effect on how long it takes for liquid to be emptied from the stomach, some sports drinks can cause fullness and bloating since they stay in the stomach longer than pure water. Carbonated beverages such as sodas and diet drinks also stay in the stomach too long and offer no nutritional value.  Any drink containing caffeine will cause the kidneys to lose too much water.
How do you know if you are getting enough water?
  1. Check your urine. If it is clear to pale yellow in color, you are hydrated. If it is dark yellow or seems concentrated, you should drink more water.
  2. Pre-hydrate. Drink plenty of water in the two hours before the workout and 16 ounces just prior to work-out. 
  3. Drink before you are thirsty, at least every 15 minutes during exercise. Thirst is a signal that you waited too long to drink.
  4. Drink again after you finish exercising. This will insure that you do not become chronically dehydrated.