Can drinking a lot of water be fatal?

Question

I vaguely recall having heard that drinking too much water can, over time, prove fatal to the human body.

Nothing special about the water; not distilled or de-ionized or anything … just plain ol' water.

Now the reason that accompanied this "fact", was that drinking too much water serves to dilute, and thereby, disrupt the electrolyte balance in all (living) body tissue. This in turn, messes with the sodium-potassium pump present in cells leading to loss of functionality of cells.

Now I can't seem to find the source of that information, but I do recall it wasn't particularly trustworthy.

So what I want to know is:

1. Is it true, that drinking a lot of water can be fatal?

2. If so, is it because the electrolyte concentration inside and outside cells are "diluted"?

3. Does this affect all (living) tissue equally?**

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Edit:

I fail to see why this was put on hold as a personal medical question. I vote to reopen this on the grounds that it does not:

a) Ask for advice on treating water intoxication

b) Suggest, promote or request, in any way, alternative forms of medicine.

Answer 1

Based on what I gathered from this Wikipedia article, Yes.

Drinking copious amounts of water can prove fatal. The proper term is "Water intoxication".

When you start taking in a lot of water (by "a lot" I mean more water than your body can excrete via sweat or urine), the interstitial fluid that bathe the cells that form your (living) tissue end up getting "diluted", i.e- the concentration of ions like $\mathrm{Na^{+}}$ is greatly reduced. The result? The concentration of ions in the interstitial fluid is far lower than the concentration of ions inside the cells it surrounds. Thinking of this in another way; the concentration of water in the interstitial fluid is far higher than the concentration of water inside the cells.

Ever soaked dry raisins in water? Over time they begin to absorb water and swell up as a consequence of the concentration gradient set up between the tissue in the raisin (Low concentration of water) and the water in the bowl. This phenomenon, where water flows from a region of higher concentration (of water) to a region of lower concentration (of water) across a semi-permeable membrane is called osmosis.

It's pretty much the same thing in the case of water intoxication. A concentration gradient has been set up between cells and the interstitial fluid that surrounds it. So water begins to flow into the cell, and the cell swells up quite a bit, resulting in a build-up of turgor pressure

This increase in turgor pressure will be seen to varying degrees in all sorts of (living) tissue, especially tissue that is highly vascular. An important example would be neural tissue, particularly that in the brain. This swelling up of tissue results in an increase in intracranial pressure which can lead to loss of functionality over time. This is what makes water intoxication so lethal.

There isn't really much about the chemistry of water that's responsible for this, apart from osmosis that is.

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Addendum:

Drinking a ton of water isn't the only way for water to build up in potentially lethal amounts in the body. Hyponatremia, which refers to a condition of low (below-normal) sodium levels in body fluids, can also lead to water accumulating in the body in excess.

Answer 2

Yes. See Jury Rules Against Radio Station After Water-Drinking Contest Kills Calif. Mom

The husband of a California woman who died after participating in a radio station's water drinking contest said he hopes a jury's $16.5 million compensation award following a wrongful death lawsuit will send a message to other corporations dealing with the public.

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[She] drank nearly two gallons [7.5 l] of water in over three hours

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A coroner ruled that her death was due to water intoxication.

For more information on the subject see Fatal water intoxication Journal of Clinical Pathology 2003 Oct; 56(10): 803–804., which discusses and earlier fatal case:

Water intoxication provokes disturbances in electrolyte balance, resulting in a rapid decrease in serum sodium concentration and eventual death. The development of acute dilutional hyponatraemia causes neurological symptoms because of the movement of water into the brain cells, in response to the fall in extracellular osmolality. Symptoms can become apparent when the serum sodium falls below 120 mmol/litre, but are usually associated with concentrations below 110 mmol/litre. Severe symptoms occur with very low sodium concentrations of 90–105 mmol/litre. As the sodium concentration falls, the symptoms progress from confusion to drowsiness and eventually coma.

There have also been several US military deaths due to excessive water consumption as reported in Death by water intoxication Military Medicine 2002 May;167(5):432-4.