In addition to Terri’s response I would add that water is essential for repacking glycogen into the skeletal muscles. It takes 3 grams of water to pack 1 gram of glycogen. Glycogen, the storage molecule for glucose, is obviously critical for vigorous and/or sustained exercise. One point to keep in mind is that a muscle only metabolizes fatty acids in the mitochondria if there’s adequate glucose available. If a muscles “runs out” of glycogen further contraction won’t occur. Runners call this “hitting the wall,” cyclists “bonking.”
Another important point is consume water in small amounts (1-2 oz) at a time as this allows the water to move from the digestive tract into the bloodstream, where it’s needed. Drinking large volumes all at once only challenges the kidneys to filter a substantial volume and spill it in the urine.