Athletes participating in ultra-events know the risk of getting the water-sodium balance in their body out of balance. Who would have ever thought it is possible to die from drinking too much water? But the fluid-sodium balance in the body is very important. Even small deviations can curtail athletic performance. Hence the proliferation of "sports drinks." However, there is controversy as to whether and when such drinks are actually necessary and/or useful. A good discussion about Hyponatremia relative to ultracycling is given, but it applies to any extreme physical effort. Excellent hydration information is found on this site. Basic, simple suggestions are found here.