distilled vs deionined water conductivity

[pippo]

People,

 

I always figured that the 2 methods for purifying water were about the same when comparing the end result- 2 means to the same end product. I know DI can get down to 18 megaohms resistivity at the service point, and after even a few minutes, it jumps to say, 0.2-0.5 u Mhos conductivity, which is still pretty clean water.

 

Someone is now telling me distilled is what I need because DI is too "corrosive". Distilled may be 1-10 micromhos of resistivity, where di is usually less than 0.5 or so. Anyone have experience in this arena?

[fiveworlds]

same end product

 

Not at all. They are two completely different processes. Distilled is boiled. Deionized is run through an ion exchange resin. Neither is perfect Distillation will not remove liquids with a similar boiling point(This may sometimes occur between a range of pressures changing the pressure may effect the boiling points of both liquids differently http://lorien.ncl.ac.uk/ming/distil/distilpri.htm). Deionized will not remove non-ionic particles.

Edited September 27, 2014 by fiveworlds

[pippo]

Not at all. They are two completely different processes. Distilled is boiled. Deionized is run through an ion exchange resin. Neither is perfect Distillation will not remove liquids with a similar boiling point(This may sometimes occur between a range of pressures changing the pressure may effect the boiling points of both liquids differently http://lorien.ncl.ac.uk/ming/distil/distilpri.htm). Deionized will not remove non-ionic particles.

 

I am aware they are 2 different processes, as I stated (2 means to same end product), although, technically, they are not same end product as you stated. But, only insofar as one can measure the difference.

 

Your link is informative. But real world, our tap water contains almost no dissolved "solvents" to worry about. Trace pesticide residues are in the parts per trillion, if even detectable. Even so, most solvents have different boiling point as water. So the solvent at the same distillation temp is not relevant.

 

So, to my original point, what should one expect in conductivity between the 2?

[fiveworlds]

So, to my original point, what should one expect in conductivity between the 2?

 

Pure Water is a bad conductor. It is dissolved particles within the water that cause it to be conductive. Electrical conductivity of ultra-pure water is 5.5 × 10⁻⁶ S·m⁻¹ (18 MΩ cm in the reciprocal terms of Electrical Resistivity) and is due only to H⁺ and OH^- ions produced in the water dissociation equilibrium. I would believe it would depend largely on the water you started with.

Edited September 28, 2014 by fiveworlds

[John Cuthber]

It is difficult to distil water in such a way that you prevent CO2 from the air dissolving in it.

That will significantly increase the conductivity.

[CharonY]

IIRC the conductivity at equilibrium with atmospheric CO2 is about 1 uS/cm (and slightly acidic pH, around 5-6). The some obviously applies to deionized water when in contact with the atmosphere.