During the time of running staying hydrated is critical to your running performance and, more importantly, for preventing heat-related illnesses. Athletes may suffer from fatigue, headaches, decreased coordination, and muscle cramping due to dehydration. Other heat-related illnesses like heatstroke and heat exhaustion have even more serious consequences. All runners need to pay attention on how much they're drinking before, during and after exercise and what they are drinking.
Pre-Run Hydration is essential for runners. Assume that you're doing a long run or race that is more than 8 to 10 miles. Then it is vital to make sure you're well-hydrated during the few days leading up to your long run. If you void large volumes of pale urine at least six times a day that means you are well hydrate. In the days leading up to your long run (or race), drink plenty of water and nonalcoholic fluids. Alcohol can dehydrate you and also prevent you from getting a good night's sleep. It's not a good decision to run with a hangover because it will make you dehydrated when you start your run.
Second important thing is you have to drink at the time of running. The present advice about hydration and running is very simple -- try to drink to thirst. It is known from scientific reports that drinking when you're thirsty can help prevent under hydrating which can lead to dehydration and over hydrating. That can lead to hyponatremia mean low blood salt level due to abnormal fluid retention.
Though the above guidelines are the fundamental rules of thumb, it's important to remember that everyone's fluid needs vary. There is several people sweat more than others. You need to know your sweat rate to determine how much liquid you have to take during a run or race. That can vary between 1 to 4 quarts per hour. You have to weigh yourself nude before and after a timed training run. One pound of weight loss equals 1 pint of water loss. Calculate your sweat rate and use this to determine your fluid needs during a run or race. For example, if you lose 2 pounds during an hour run, that's 2 pints or 32 ounces. Thus, you need 8 ounces of water or sports beverage every 15 minutes. Make a note of the weather conditions on that day, and remember that you may need to adjust your consumption in different condition. To see how different conditions affect your sweat rate, you need to measure your sweat rate on another day.
Last thing is post-run hydration. Always remember to rehydrate with water or a sports drink after your run. You have to drink 20 to 24 fl oz. of water for every pound lost. You need to keep rehydrating if your urine is dark yellow after your run. It should be a light lemonade color.