demiurge1138 said:Exceedingly rare. Most of the cases of "water intoxication" on record are due to drugs, especially in recent years Ectasy. If you drink way, way, way too much water without being able to let it pass through your system, the amount of solutes in your body decreases. Since the electrolytic effects that solutes have allow your nerves to work, this is a bad thing.
Hypernatremia is the technical name for the condition. A woman running the Chicago Marathon here a few years ago died from it.
But, as demiurge says, it's very very rare.