Water is one of the most important nutrients an athlete can consume. Almost 60% of total body weight is water. It helps to maintain body temperature, improve digestion, and helps with circulation and excretion of wastes. Sweating is how the body regulates its temperature. If an athlete does not drink enough water, they are not able to sweat adequately and their body temperature will rise. This can negatively impact their physical performance and cause dehydration. Even a very small amount of dehydration can affect their athletic performance. And thirst is not an indicator of dehydration. It can happen before an athlete even becomes thirsty.
The body will pull water from its reserves when it's stripped of liquids to maintain a safe body temperature. If the body is chronically low on water, a variety of hormonal changes can occur. Caffeine, alcohol and diuretics can all drain the body of water, and extra water should be taken to avoid an imbalance.
The small intestine can absorb water at a rate of 8-10 ounces about every 20 minutes. Drinking cold water is better because it will enter the small intestine faster. Take small sips before, during, and after your workout. Make sure not to drink large amounts all at once. Space it out.
The only way for an athlete to prevent dehydration is to make sure they are properly hydrated before, during, and after training. Customize your water intake to the sport you will be training in. Make sure you have water readily available during training and make sure you drink enough water before and after training. Know what your sweat rate is. It can be different for different people. Know how much fluid you will need to replace. A good rule of thumb is to drink about 20 ounces of water for every pound of weight lost because of sweating.
If you think that water is just too plain and boring, then try a good sports drink with your favorite flavor. The most important thing is to make sure you replace fluids and avoid dehydration. If you have to have the flavor to make sure you drink more water, then whatever works for you is best to ensure you do not suffer dehydration.
If you have signs of dehydration, like weakness, headache, thirst, dizziness or chills, not only is your athletic performance going to suffer, but you are putting yourself in danger of a heat related problem. It's better to avoid that in the first place by making sure you are drinking enough water to stave it off in the first place.