Can you drink too much water?
When your kidneys are unable to excrete the excess water, the electrolyte (mineral) content of the blood is diluted, resulting in lower-than-normal sodium levels in the blood, a condition called hyponatremia. Endurance athletes, such as marathon runners, who drink large amounts of water are at higher risk of hyponatremia. In general, though, drinking too much water is rare in healthy adults who eat an average American diet.
As for how much you should drink, most healthy individuals can let their thirst be their guide. — Philippe Desplat, Doctor of Osteopathy, medical director, Valley Medical Group, Dumont
— John Petrick