When you are excercising hydration is extremely important. Most cramps, pains, and other problems come from not being properly hydrated. This can be easily fought by starting to drink water well before you run.
Water takes a while to work its way into your system. When you drink water after you run it takes a while to hydrate you and in that time you will feel thirstier. Drinking water before you run gives your body water to process while you are running and to replenish moisture lost to sweat.
Staying hydrated helps you to stay cool. When you drink water before you run you stay cool for longer during your run. This means that drinking water before hand can actually improve your running performance. Water also keeps you more hydrated than anything with sugar in it making it the best choice for staying cool.
Keeping your muscles hydrated can also improve your performance. When you cramp up or get a stitch in your side it is because your body needs something. Oftentimes this something is hydration (or possible oxygen - check your breathing). This kind of pain takes away from your performance causing you to stop and lose your motivation.
Drinking water before you run also aids in keeping you healthy on the inside. Sweat is impurities leaving the body. Your body needs hydration to sweat so not keeping yourself hydrated can keep you from releasing those impurities. Giving yourself fuel to sweat with running can actually improve the results you get from running and protect your body from damage.
Quenching your thirst is just one of the many benefits of water. Preventing you from becoming exhausted and causing yourself damage are two big benefits to drinking water before you begin. This small tip can help improve your performance and preserve your future performance as well.