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I know that water with some ions dissolved is a good conductor. I wonder whether it is true for pure water?

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    $\begingroup$ This sort of question shows a severe lack of effort on the part of the poster. $\endgroup$ – Carl Witthoft Oct 10 '15 at 21:14
  • $\begingroup$ Indeed, since DI water is characterized by its resistivity. Although DI water is not pure either... $\endgroup$ – Jon Custer Oct 10 '15 at 21:23
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    $\begingroup$ I'm voting to close this question as off-topic because it shows insufficient prior research $\endgroup$ – John Rennie Oct 11 '15 at 11:05
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No, pure water is not a good conductor at all, though the conductivity is not zero.

According to the LennTech webpage Water Conductivity:

Pure water is not a good conductor of electricity. Ordinary distilled water in equilibrium with carbon dioxide of the air has a conductivity of about $10 \times 10^{-6}\ W^{-1}m^{-1} \ (20 dS/m)$.

The reason is that there are no abundance of ions in pure water to conduct the electricity.

A table of comparisons is provided from the Physical Process Modelling website:

enter image description here

Note: the entry Water (distilled) is not the purest that water can be, see Ultrapure water which has significantly less conductivity than distilled water. But this table is given as a comparison with other materials.

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  • $\begingroup$ Is it good or bad compared to other materials? What about water in isolation from CO2? $\endgroup$ – Anixx Oct 10 '15 at 21:14
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    $\begingroup$ lenntech.com/applications/ultrapure/conductivity/… gives a few things to compare with. $CO_2$ would increase the conductivity quickly because in water it converts to carbonic acid, which contributes ions and thus conductivity. $\endgroup$ – Gert Oct 10 '15 at 21:18
  • $\begingroup$ @Anixx I have added a table with comparative information $\endgroup$ – user94040 Oct 10 '15 at 21:46
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Even the purest water has some, very limited conductivity.

That's because water undergoes an auto-dissociation reaction:

$2H_2O(l) \rightarrow H_3O^+ (aq) + OH^- (aq)$.

The oxonium ($H_3O^+$) and hydroxide ($OH^-$) ions are charge carriers and allow limited current to be carried. But the total concentration of both ions together in ultra pure water is only about $2 \times 10^{-7}\:\mathrm{mol dm^{-3}}$, which is a very low value compared to ion concentrations in e.g. tap or river water.

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  • $\begingroup$ What is this conductivity compared to other materials? $\endgroup$ – Anixx Oct 10 '15 at 21:14
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    $\begingroup$ lenntech.com/applications/ultrapure/conductivity/… gives a few things to compare with. $CO_2$ would increase the conductivity quickly because in water it converts to carbonic acid, which contributes ions and thus conductivity. $\endgroup$ – Gert Oct 10 '15 at 21:18

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