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.

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    He said it would kill me, so I drank it. Love it! – Rory M May 13 '12 at 18:06
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    @RoryM that is precisely what happens when kids are told about dangerous stuff..... – The-Ever-Kid May 14 '12 at 11:43
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    An empirical if not wise approach – David LeBauer May 16 '12 at 4:34
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    For the opposite scenario, see:… – Bitwise Oct 25 '12 at 13:40
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    "experimental" tag added - he did test the hypothesis of his friend! – Volker Siegel Sep 26 '14 at 10:49
up vote 44 down vote accepted

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.

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    But if you drink distilled water and eat salt, there should be no effect? – David LeBauer May 16 '12 at 4:36
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    As long as you have the right salts and the right quantities, then yes. There is the possibility of still drinking acidic distilled water to worry about, but it should not be too dangerous (similar pH to sodas). – user560 May 16 '12 at 12:00
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    This answer was borderline wrong. Specifically I take issue with Drinking only this kind of water will be fatal because it is highly hypotonic as you've found out -- I drank only distilled water for over 5 years with no ill affects whatsoever. As you explain later in the answer, it's about salt balance, and there's more than enough salt in food (at least in America where I am) to compensate for drinking distilled water. So, maybe you'd die from drinking only distilled water and not eating, but I can confirm that drinking distilled water is not a sure path to death. – Josh Sep 25 '14 at 5:57
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    "drinking a little bit is not generally fatal" ? when was it fatal? no references here... clearly we'd like some for this part. – shigeta Sep 26 '14 at 13:56
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    -1. I am pretty sure distilled water is neutral, not acidic. Can you provide a source for your claim? – March Ho Jul 16 '16 at 10:10

I'm extremely skeptical of @leonardo's answer. I suspect that what would happen if you drank only distilled water is nothing perceptible. The only place where concentrations of distilled water would ever be high enough to conceivably matter is in the tissues of the mouth and throat, and even there, the effect would be temporary.

Compare drinking 8 glasses of either distilled or tap water every day. With tap water, you're looking at less than 200 ppm of Mg, Na, K, and Ca combined. That's less than 400mg of total mineral content per day. Given that the combined RDA of all of those minerals is on the order of 7g for an adult male, this is not nothing, but it's certainly small. Your dietary intake of these minerals probably varies by more than this daily, and your intestines, kidneys, sweat glands and mineral storage organs (like your bones and muscles) are constantly maintaining the mineral blood levels within a very narrow range, despite handling a throughput of several pounds of water and food daily. They might have to work slightly harder to manage this range if you drank nothing but distilled water, but in a healthy adult, normal intakes already vary by more than this amount without major problems. For example, the average American consumes more than 3.4 grams of sodium daily, while a low-sodium diet is on the order of 2g. Low-sodium diets have been widely studied in the medical literature, and are considered safe.

As for pH, the lowered pH is caused by increased carbon-dioxide absorption to form carbonic acid. Just as carbon dioxide is more soluble in distilled water, it is less soluble in stomach acid, and may be burped out. Would you die of acidosis from drinking seltzer water all the time? If that were the case, I'm sure there would be big health warnings about drinking soda, while it seems relatively benign. Furthermore, your body produces and excretes (through the lungs) around 1kg of CO2 daily, dwarfing any extra CO2 you might get by drinking distilled water. If the small amounts of CO2 found in distilled water were dangerous, jogging would be invariably fatal.

If you were to drink nothing but distilled water, and eat no food, you probably would die of hyponatremia within a few weeks. But you would also die of hyponatremia if you were to drink nothing but tap water, though perhaps slightly more slowly.

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    +1. I'm with Recursivelyironic. Most of the ions in our diet come from the foods we eat, not the water we drink. Unless you're sucking down softened water in the shower, your salt and calcium should be coming from your big dietary sources - fruit, veggies, meat, seasonings, etc. – MCM Feb 13 '13 at 12:36
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    +1 Unless you drink to hyperhydration, which is not what the original question was about at all, distilled water will not cause problems at all, literally zero problems. You can buy distilled water by the gallon at the grocery store for goodness sake, and people commonly have reverse osmosis filters for their drinking water in their sinks, producing almost exactly the same effect. – Jason Patterson Sep 25 '14 at 14:19
  • Well, there are big health warnings about drinking excessive amounts of soda. But not because of its acidity. – David Richerby Nov 29 '16 at 13:24

I'm not sure why no one mentions this, but any food you eat would negate this effect entirely.

Assuming then, that you had no food, the lack of minerals in this pure water would simply be another deprivation for your body. The intestinal track actively reabsorbs ions, countering this. However, in this water-only deprivation, those mechanisms might fail as some are glucose dependent.

In general, if you want to know "exactly how much of X on an average is needed to be consumed to cause death", then the magic search term for Google is "LD50", that is the dose that kills 50% of victims.

I've seen the LD50 for water quoted as 90ml/kg for rats (that is, 90 ml per kg of body mass), for example on this safety data sheet. I presume that figure comes not from theorising about salt intake, but from giving measured quantities of distilled water to rats and counting how many die.

It's likely of the same order of magnitude for humans. Unlike many "poisons" it's not about subtleties of liver chemistry that will vary by species. What killed the rats was the swelling by osmosis of cells and tissues that they didn't want swelled.

For a largeish human that dose is 7 litres, approx 14 pints, drunk at a sitting. Which is fairly unlikely in a school chemistry lesson. Besides, with effort you could drown in less than that!

The distilled water in your chemistry lab has a relatively much larger chance of killing you for some reason other than its inherent toxicity (although it's still fairly unlikely in absolute terms). For example if it's stored for a while there could be legionella in the tanks. Probably best not to drink it, just as it's best not to drink any water that may have been sitting around for weeks in an unsealed container.

Definitely don't drink other stuff from the labs that your friend tells you is poisonous, because some of it really is. In particular the one everybody thinks of (because, like the water, it's similar to something they know about): lab ethanol can have methanol as an impurity, and may well have had benzene intentionally added because that's an easy way to get the last 4.5% water out that otherwise cannot be removed by distillation. A mouthful of ethanol isn't normally lethal (although it might be illegal), whereas methanol and benzene are both "properly" toxic in the sense that a few grams will kill you.

By the way, I can confirm that in my school days I obtained the same experimental result you did.

protected by Community Mar 24 '13 at 19:20

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