Creatine binds to water (making less water available to your muscles) and allows your muscles to work harder (which makes them need more water). So if you're not drinking a lot more water when you're taking creatine, you will get cramps from either dehydration and/or muscle overuse.
But once you're past the loading phase for creatine and getting sufficient hydration, it's supposed to lessen cramps because the water bound to creatine also becomes available for use again as the creatine is used by the body.
But the cramps are really debilitating, as in random back muscle locks up debilitating, so I thought it best to just give up on this.
So the amount of creatine changes the rate as which water is loaded into the cell, but the total amount of water needed is calculated based on your muscle mass. The figures I've seen is 2L extra water (spread evenly, not all at once) for a normally recommended 5g daily creatine intake during loading (which typically takes a month at 5g/day dosage).