Hydration

  Ever worked out and decided not to drink any water?  Go try it: you'll feel less energetic, get lots of cramps in your abdomen, have no energy, and want to go in the corner and curl into the fetal position.  Sound like fun?  No.  Let's talk about why it is a glorious and spectacular idea to hydrate yourself (and by hydrate, I mean the utilization of water, or such things as Gatorade).
  Our bodies are made of 65%-70% water.  As we go about our days, notice how sometimes you have to go to the restroom?  Well, ya do, and you're losing water.  You also lose water when you sweat, or when you spit, or when you blow your nose or you sneeze.  Therefore our bodies need water during the day so that we can fuction properly.  We should be drinking at least 1/2 our weight in ounces of water a day.
  In regards to sports and/or exercise, when we sweat we absolutely lose water.  We need to replenish those liquids otherwise our bodies won't be able to continue exerising - and you'll probably vomit or pass out.  Not such a good thing...
  Your muscles also go through more hypertrophy (muscle cell expansion) because of lots of water!  That means the more water you drink, the bigger your muscles can get.  That is another topic entirely, but do know that if your goal is large muscles, drink tons of water during your workout.