Why is too much water dangerous?

Jennifer Strange had taken part in the "Hold Your Wee for a Wii" game, which promised the winner a Nintendo Wii. Afterwards she reportedly said her head was hurting and went home, where she was later found dead. Initial tests have shown her death is consistent with water intoxication.

Here is the explanation:

Water enters the body when we drink and is removed primarily in the urine and sweat. If you drink too much water, eventually the kidneys will not be able to work fast enough to remove sufficient amounts from the body, so the blood becomes more dilute with low salt concentrations. The water then moves from the dilute blood to the cells and organs where there is less water.

Professor Forrest likens this to the effects seen in science-class experiments. "If you put salty water on onion skin the cells will shrink, if you put too much water on it the cells will swell," he says. This swelling is a problem in the brain.

"When the brain swells, it is inside a bony box so has nowhere to go," he says. "The pressure increases in the skull and you may get a headache. As the brain is squeezed it compresses vital regions regulating functions such as breathing." Eventually these functions will be impaired and you are likely to stop breathing and die.

[Source: splush][More: BBC]