I don't have enough information to cite a cause, but people often erroneously blame a lack of water or fluid consumption for cramping. In truth, hydration is much more a product of the proper ratios of body salts and electrolytes (sodium, magnesium and potassium) than water or any other fluids. These minerals can be leeched from the body by different drug combinations, likely related to what’s happening to you. If however salts & electrolytes are being inefficiently replaced, the presence of high water intake would serve only to further exacerbate an already negative condition by washing away the remaining salts, i.e. Water Intoxication or Hyponatremia…an osmotic attempt to rebalance internal and external cellular water levels in the absence of enough electrolytes:
http://chemistry.about.com/cs/5/f/blwaterintox.htm
http://sportsmedicine.about.com/od/h...ponatremia.htm
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Regardless, the best way to resolve your condition is to buy and start drinking Gator/Powerade which as you know contains concentrated liquid based (for faster absorption) electrolytes. It would also behoove you to purchase these minerals in tablet form from a drug or health food store for sustained release and protection.
Here’s a recent and EXTREME example that many of you may remember, of what can happen when these minerals are inadequately replaced and large amounts of water are rapidly consumed…again proving that water though important, is not the central component to hydration:
http://www.cbsnews.com/stories/2007/...n2369761.shtml
http://www.msnbc.msn.com/id/16614865/
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L-Taurine is believed to play role in governing these minerals but scientists simply aren’t sure exactly what goes on there as even an exhaustive secondary data search on this amino acid will illustrate. But adding it surely wouldn't hurt!