I can't speak for every person or every situation, but some of the time, charlie horses and other types of muscle cramps could be due to dehydration. I used to get HORRIBLE charlie horses in my calves and other muscle cramps, but when I started drinking more water, they've since disappeared. And I've found, that on very rare occasions when I still get charlie horses, it's because I haven't drank enough water that day.
Just a thought I wanted to toss out there