Deionized-vs-distilled water

Had a quick look through and couldn’t find them in the same topic, a number with distilled and a number with deionized…what ones better?

I thought the water hade to be non-conductive or as low as possible, where this link says distilled water is conductive?

“Care must be exercised when using DI water. The very lack of ions also makes this coolant unusually corrosive. Called the universal solvent, DI water is one of the most aggressive solvents known. In fact, to a varying degree, it will dissolve everything to which it is exposed. Therefore, all materials in the cooling loop must be corrosion-resistant and compatible with DI water.” Quote from the link below.

As a chemist I can say that doesn’t really make any sense.

DI water is just water with the mineral ions removed. Neutral organic compounds may still be present. The lack of ions in DI and distilled water can cause extraction of metal ions from carbon steel surfaces due to the low hardness of the water. Nothing especially corrosive about it.

Distilled water is going to have mineral ions and almost all organic compounds removed.

DI water can be very pure with additional filtration and is what is used in most industrial situations that need pure water because it’s more economical to produce compare to distilled.

Generally distilled is going to be easier to get for most people and will have the best purity. It’s therefore the preferred cooling liquid.


@NedMan — would you mind editing Cooling the K40 laser tube with the difference between deionized and distilled and why distilled makes sense? A site search shows the question has come up before, including the suggestion that deionized water is corrosive, so getting a sensible answer into our getting started documentation would be awesome!

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I will take care of it :slightly_smiling_face:

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I found this article, what do you think Ned?,the%20surface%20of%20the%20steel.

That link is correct.

The corrosion aspect of DI water (and distilled water) is caused by the low mineral ion content of the water. So if carbon steel is immersed in the water it can pull ions out of the metal because there exists a large non equilibrium condition.

Stainless steel is mostly resistant to this effect. Materials other than metals will be generally unaffected as well, unless they contain leachable ions.

So it’s possible that new plastic components of your cooling system could leach a small amount metal ions initially when exposed to low ion purified water. This could offer a very small change (probably negligible) in conductivity but would fade over time with subsequent water changes.