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Is de-ionized water more corrosive to metals than tap water? I have read that it "wants" the removed ions back and will aggressively take them from any available source.

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  • $\begingroup$ Where did you read this claim? $\endgroup$
    – user15489
    May 19 '15 at 18:59
  • $\begingroup$ santiago asks where I read this claim? Two places-Wikipedia-Purified water-reference 19 "Health risks from drinking DI water" Kozisek,F. (2005), and overclockers.com/pc-water-coolant-chemistry-parts 1 and 2. $\endgroup$
    – Bobby K
    May 19 '15 at 21:51
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The Wikipedia article merely states that sole consumption of purified water may deplete some electrolytes through normal excretion and lack of replacement, not that it somehow "wants" the minerals.

As a matter of fact, pure, deionized water is much less corrosive to metals and is often used in closed systems to prevent corrosion because it helps prevent galvanic (electrolytic) corrosion.

Automotive coolant antifreeze contains specific corrosion inhibitors safe for aluminum and iron parts, but if water needs to be added, it should be distilled water, to prevent galvanic corrosion.

People living in northern climates often encounter corrosion of vehicles due to road salt, and learn to wash vehicles with tap water to remove the salt (high-purity or distilled water would be better, but not cost effective).

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  • $\begingroup$ Deionized and distilled water are two very different things. Deionized is much less corrosive than distilled water, since deionized still contains many solute species, just not easy-to-ionize ones like sodium. $\endgroup$
    – Jon Custer
    May 19 '15 at 23:15
  • $\begingroup$ True... but for the purpose of removing road salt, either would work, but would be too expensive to be practical (unless for washing a cincours d'elegance vehicle). $\endgroup$ May 20 '15 at 18:55

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