Don't OD on [H.sub.2]O

WATER SEEMS STRAIGHTFORWARD enough. You can see through it. Nothing to hide. Keeps you alive. A solid citizen in the nutrient world. Morgan Freeman would play it in a biopic. Ah, but lurking behind that noble facade is a hidden danger, says USA Track & Field, which has issued new guidelines on fluids.

HYPONATREMIA IS a possibly dangerous condition in which too much water intake dilutes the sodium level in the blood. It's most often caused by prolonged exercise--four hours or more--and is made worse by the failure to replenish salt. A severe case may include seizures, respiratory arrest, even death.

FOR ATHLETES, particularly for those who take more than four hours to do a marathon, USATF recommends consuming fluids equal to your sweat loss. Runners should be guided by their thirst rather than the old-school principle of drinking as much as possible.

THE ORGANIZATION also prefers sports drinks spiked with sodium and other electrolytes instead of plain water, and suggests drinking eight to l0 ounces of fluid every 15 to 20 minutes during a race. Don't take anything containing ephedra, which could increase the risk of heat-related illness. And avoid nonsteroidal anti-inflammatories 24 hours before race time and at least six hours after finishing.