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I am studying different means of collecting water for consumption. From resources available on Internet, I understand that distilled water is not advised for regular consumption because of the lack of minerals and salts, while rainwater can be consumed if not overloaded with unwanted chemicals.

What confuses me is that I know water to be pouring down from clouds, which is water vapor turning into droplets through condensation. To me, this looks to be exactly the same as the process of distillation, i.e. evaporation and condensation of water.

So is my assumption about rainwater formation wrong? What is the difference between rainwater and distilled water? What causes this difference to happen?

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    $\begingroup$ While there are some internet memes that advise against drinking distilled water, there is no real problem with doing so. The minerals in most water are only ever present in very small amounts with barely measurable effects on health (very hard water is known to marginally lower heart attack rates) so their lack is not going to be significant either. $\endgroup$ – matt_black Nov 4 '12 at 0:05
  • $\begingroup$ @matt_black: perhaps you would be interested in this discussion then, skeptics.stackexchange.com/questions/5484/… $\endgroup$ – Benjamin Nov 4 '12 at 8:57
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    $\begingroup$ Not everything on skeptics is reliable. Read Rex Kerr's answer and the comment about the provenance of the study that supposedly proved it. Or read my answer to this question and see some proper statistics on the small differences to people caused by different mineral contents. $\endgroup$ – matt_black Nov 4 '12 at 10:08
  • $\begingroup$ Agreed. Nutrition is a tough science, because it's just tough to experiment, since manifold ingredients end up to make big soup in the body. Not even mentioning metabolism are not all the same. BTW Do you know a way of remineralising water other than adding a package of minerals? $\endgroup$ – Benjamin Nov 4 '12 at 14:13
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    $\begingroup$ ""way of remineralising water other than adding a package of minerals?"" ROFL $\endgroup$ – Georg Mar 21 '15 at 20:52
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Rain water passes through the atmosphere and picks up whatever is present there, including particulates such as dust, trace amounts of atmospheric gases, nitrates and nitrites, and so forth.

Rain water is relatively low in mineral content. In practice, people drink rainwater from streams and wells, where it has had ample opportunity to pick up minerals from soil and rock.

https://www.google.com/search?q=rain+water+composition

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  • $\begingroup$ The YouTube channel minute earth even explains why it is impossible for rain to form without dust or minerals in the middle of each drop, but sadly I can not post the link at the moment. $\endgroup$ – Aubrey Champagne Nov 28 '15 at 3:19
  • $\begingroup$ Do you know of better sources for this than "lmgtfy"? Well-regarded published papers, for instance. It would also help for this answer to include some quantitative information - both rainwater and distilled water will contain some amount of impurities in practice, so what we really care about is how much. $\endgroup$ – Nate Eldredge May 12 '16 at 22:11
  • $\begingroup$ @Nate: There are several well-regarded studies in that Google Search. I'm happy to enumerate all of them in my answer, but the Google Search is maintained and updated automatically. $\endgroup$ – Robert Harvey May 12 '16 at 22:32
  • $\begingroup$ Indeed. But part of the purpose of SE is to get answers from experts. Google can tell us what studies there are, but it can't give us an expert opinion as to whether they are relevant, reliable, appropriately conducted, etc - that's where you come in. There's also a preference for answers which are not "link-only" but give a summary of the conclusions, thus helping to avoid link rot. $\endgroup$ – Nate Eldredge May 12 '16 at 22:36
  • $\begingroup$ W@Nate: Well, I'm not actually an expert, but I do know enough about the rainwater ecosystem to answer the OP's question at his level of expertise. If the OP wants detailed composition analyses (he didn't ask for them), then someone else is probably better qualified to render those. Properly distilled water really shouldn't contain anything in significant amounts except water molecules, though I suppose you could contemplate copper atoms picked up from the condensation tubing. $\endgroup$ – Robert Harvey May 12 '16 at 22:38
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Rain water contains very low amounts of salts and other nitrates but it takes in any gas present in air. That is why acid rain occurs when the air is polluted. The air contains oxygen so people recommend the rain to be consumable as it has lots of oxygen contents in them. But distilled water does not contain any minerals in them, so it is not recommended for consumption because of lack of minerals.

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