Still thirsty? If drinking fluids doesn't relieve your thirst, you may have a health condition such as diabetes. See your health care professional right away.

Too much of a good thing. In very rare cases—chiefly among marathon runners—drinking too much fluid leads to a life-threatening illness, hyponatremia. This occurs when sodium levels in the blood fall too low. It happens chiefly to athletes who have run for more than four hours and gained a lot of weight during the race from drinking.