How safe is drinking distilled water?

Question

Are there any adverse effects of drinking distilled water (possibly obtained melting snow or using other survival techniques like a solar still)? Maybe dehydratation, diarrhea...? Some people even claim that it can induce embolism and red-cells death.

For instance, there is the saying pure water, as it goes in, it goes out.

So many people recommend mixing distilled water with some salts ¹. As far as I've read, the danger is mostly a myth.

Any personal experiences?

There is a related question at Skeptics.SE: Does drinking distilled water remove needed minerals from your body?

¹ As an anecdote, some mountaineers and scouts used these salts to mineralize and oxigenate water:

Answer 1

The effects of drinking distilled, deminieralized, deionized, and many other forms of water purification have been thoroughly studied and despite the research, the jury is still out on the subject, with regards to temporary usage.

As far as adventuring goes, it appears it does not matter, as long as the water you are drinking is microbiologically and toxicologically safe, it will be fine. If you drink distilled water all day every day, you may after awhile have a mineral deficiency, though supplements and diet can solve that.

However, distillation of any water recovered in the field requires an enormous amount of energy compared to other methods of treatments. So much so that it is completely impractical to distill water in the wild, you will destroy whatever campground you go to, collecting enough firewood to distill enough water to drink, in addition to the equipment you'd need.

As for the concern about needing salts, that is not a myth, but it only is an issue in some environments: those were you sweat a great deal and drink a lot of water. In those situations, e.g. desert camping, hyponatremia can be a serious concern. However, elsewhere, such as backpacking in the cool mountains, is pretty much never going to be an issue.

Answer 2

• Distilled / deionized (as for lab purposes) water tastes stale. So do reverse-osmosis drinking water, and cooked water: this is attributed mainly to the lack of CO₂ / HCO₃⁻ compared to fresh ground / tap drinking water.

• Yes, you can encounter distilled water in outdoor situations. In winter it lies around on the ground as white powder...
  Lots of people have survived melted snow as primary water source for winter tours.

• Unless you happen to drink from mineral wells, the difference in minerals between drinking water and distilled water is very small. (Mineral waters sold as such can actually contain more salts than would be allowed for tap drinking water - check your water legislation).

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A few thoughts about particular ions:

• The ion of which we need highest amounts is Na⁺ (particularly if sweating a lot). However, we get that usually through salt in the food rather than salt in the drinking water. Next may be K⁺, which is supplied by plants/vegetables.

• I think the mineral that we take up from drinking water is Ca²⁺. But I've not heard of concerns about Ca²⁺ supply for people who have to live with reverse-osmosis water, so presumably the usual food has large enough supplies of that as well (the agent of concern is vitamin D, which is needed for the uptake).

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• Dehydration means that lack of water is the primary concern: salt concentrations in the body are too high and need to be diluted. Thus, in dehydration situations, distilled water is unproblematic.

• Of course, a water loss (e.g. due to sweating) can be accompanied by salt losses which need to be replaced as well. This is called lack of volume (implied: of physiological solution, i.e. in 1st approximation 0.9% NaCl in water)

• Healthy humans can realize what is needed by the distinction of being thirsty (lack of water) and salt-hungry (loss of salts). E.g., if water appeals to me more than say chips or a strong broth, the problem is the water loss and not the lack of salt.

• With diarrhea the problem is that you cannot take up water (it passes too fast). This always means that you also have a loss of Na⁺ through the guts: internally, Na⁺ is secreted into the gut volume, and water is taken up together with the resorption of the Na⁺. If that resorption is impaired, you have a dangerous loss of minerals (mainly Na⁺) as well. Diarrhea also implies that the absorption of nutrients doesn't work. Therefore, for the treatment of diarrhea, the water should contain minerals and sugar.

• I've heard the problematic of salt loss discussed a lot, but in outdoor practice, so far I've only met dehydration where the salt was not a concern: the usual food we carry comes with enough salt. I can see that problems may arise if you forget to bring salt to a wilderness trip where you live of mushrooms, berries and water. The only story I know where I think lack of salt is a plausible explanation of the problems was a tour where, due to financial constraints, the food was reported to have been fruits and vegetables collected on the way only (no cheese, no sausage/salami, no bread).
  I recall a peculiar occasion after ca. 10 days of hiking where the question "anyone wants chocolate?" was answered by "no, but is there any of the beef jerky left?" - a feeling which was shared by all of us. However, my guess is that this appetite for the jerky was less for salt but for the protein as the food had contained substantial amounts of salt as we were using dehydrated soups as the basis for the sauce to the pasta and rice which contained enough salt so that extra salt was not requested, but had had only very low amounts of meat/cheese/milk powder.
  I guess one can check that by imagining chips/salt sticks vs. a steak and check which appeals more to the appetite.

• In outdoor winter situations, the dehydration is usually rather accompanied by a lack of energy (exhaustion) than salts (uncomfortable weather => no rests to drink, neither to eat; but usually cold => less sweating, but respiratory water loss) so the proverbial tea with sugar tackles both problems.

Answer 3

Distilled water is acidic (pH lower than 7), because it absorbs carbon dioxide from the air. Tap water contains all kinds of salts that act as buffers. The acidity is not dangerous, but can be measured easily with pH paper.

It is true that distilled water is surprisingly corrosive and can eat through steel, brass or copper. Maybe a few mm a year, depending on the flow velocity. I have seen this myself in a cooling system in the lab that needed distilled water as a non-conducting coolant. If you need to use distilled water, there are special corrosion inhibitors. This is why you are not supposed to use distilled water for your car. It is not a health risk per se.

The reason is the acidity, and the fact that some of the minerals in normal water form a protective film on the metal surface. A steady flow of distilled water steadily corrode the material away till you have a leak.

From a practical point of view, the difference between distilled water and soft water is less than 100 mg of salts per liter, as most food has too much salt anyway, I would personally not worry at all. Only if you drank it for a long time and had no other source of essential minerals. Water from snow is probably heavily contaminated and has some minerals, and people have been catching and drinking rainwater forever without adding salts.

One reason not to drink commercial distilled water is that I would not touch anything that is not made in a food grade factory. The heavy metals from the corroded piping might have leached into the water, it might have been stored forever in a gas station in the same room with the battery acid. Who knows.

Answer 4

Distilling water is a just about as pure as you can get it, better than filtering. You theoretically end up with zero dissolved solids and zero bacteria, viruses, etc. It is possible, if the water has the right chemistry, for some dissolved chemicals to condense along with the water (like methanol can in an ethanol still), but that's not very likely.