Drinking too much. If you mean "stomach" cramps it may be because your drinking too much at one time. Make sure you have hydrated throughout the day before exercise. Drink 8 ounces over the hour before exercise then drink an ounce (good mouthful) every 15 min during. Eating properly - 3 balanced meals per day- are important too.
Cramps from fatigue. Over fatigue of the affected muscle is the usual cause not drinking water. Nevertheless low potassium may play a role sometimes, so drinking emergenc c with lots of vitamin c and potassium would always be better than water.