human biology - Death because of distilled water consumption

One of my friends said that I would die if I drank distilled water (we were using it in a chemistry experiment) I gave it a go and surprisingly did not die.

I did a bit of Googling and found this

It said that drinking only this kind of water could definitely cause death, as distilled water was highly hypotonic and it would make the blood cells expand and finally explode and ultimately cause death.

I wanted to know exactly how much of this water on an average was needed to be consumed to cause death.

Answer

Drinking a little bit of distilled water is not fatal. Drinking only this kind of water and ingesting nothing else will eventually be fatal because it is highly hypotonic as you've found out.

Salt balance in the body is largely maintained by passive diffusion. Salts diffuse from areas of relatively high concentration (eg, stomach) down to areas of low concentration. For example, if you have just eaten a meal, the stomach contents are relatively higher in salt concentration compared to the surrounding tissue and the blood. Salt diffuses out of the stomach and into the stomach lining, intestines and blood. Tissues have to make sure they don't get too much salt or they will take in too much water and burst, so they have active transport mechanisms to remove excess salts and they go into the blood as well. Now that the excess salts are carried in the blood, they ultimately get filtered at the kidneys and excreted in urine. The kidneys are able to filter the salt by taking advantage of this gradient moving salt once again from high to low concentrations. The exact details are not important for this discussion, other than to know the kidneys need a highly concentrated store of salt to function.

Distilled water on the other hand, has no salt. It is pure water. Distilled water will pull salt out of the tissues because now it is the absolute lowest concentration of salt. Tissues will also take in a lot of this water because it too passively diffuses and it is hypotonic. When this happens in the blood, red blood cells tend to burst because they can't tolerate a terribly large change in tonicity, and so some red blood cells die. The other problem is also that the salt control mechanisms in the kidneys malfunction because too much salt gets leeched out of them and passed in your urine.

After drinking too much distilled water, electrolytes and important minerals get leeched out of your body and this creates electrical abnormalities in your body leading to irregular and weak heart beats (from hyponatremia and hypokalemia), poor muscle strength, high blood pressure and fatigue. Distilled water as mentioned, is fairly acidity (can be as low as pH 3 when freshly distilled) and leads to acidification of the blood (acidosis).

There is no exact amount of water that one needs to drink to die. This mode of death is related to hyperhydration/water intoxication. This can happen from over-hydrating with regular tap water, but will take longer than distilled water because of the salt content in tap water.