I would start riding with two bottles, one with water and the other with an electrolyte drink. If your stomach can handle Gatoraide, Power Aide or any other packaged sports drink then those will do but if not, there are several companies that made electrolyte tablets, mixes and pills that can be purchased at just about any bike or nutrition shop. I would alternate between the water and electrolytes during your ride and see if that helps any. If it does, I would suggest drinking more of the electrolytes and use the water for when you run out of electrolytes. I would also look into taking potassium supplements on a daily basis. If you have had a history of cardiac issues, I would check with your doctor before you start taking potassium supplements. Your doctor will be able to tell you what the maximum dosage of potassium he wants you to have. Keep yourself well hydrated and replenish the electrolytes you lose from perspiration and you should see the leg cramping subside.