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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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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. –  matt_black Nov 4 '12 at 0:05
    
@matt_black: perhaps you would be interested in this discussion then, skeptics.stackexchange.com/questions/5484/… –  Benjamin Nov 4 '12 at 8:57
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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. –  matt_black Nov 4 '12 at 10:08
    
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? –  Benjamin Nov 4 '12 at 14:13
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up vote 8 down vote accepted

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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