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DI water 13 Mohm vs 17 Mohm resistivity

2004

At what resistivity of DI water will you start to see hard water stains on glassware? I know that 15 Mohm-cm water corresponds roughly to 50-75 ppm total dissolved solids. At this purity, you shouldn't see hard water deposits on your glassware. But if the quality of the DI water drops to 13-14 Mohm-cm would this be low enough to cause stains on distilling apparatus (Calcium deposits)?

Any info is appreciated.

Newton, btw I like your PV. I have 1957 PV444.

Belinda Tomasi
Aerospace - Glendale, Arizona

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You should be OK above 10 Mohm-cm. I wouldn't expect problems above that.

James Totter, CEF
- Tallahassee, Florida
2004

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There is some inconsistency in your numbers. 15 Meg-Ohm-cm is water with a very high purity and has < 0.1 mg/L of dissolved solids. If any hardness was present,it would be a tiny fraction of a mg/L. Water of this purity,or even 10 Meg, should not leave any visible residue. If the water you are using actually is this pure, then you are probably not rinsing thoroughly enough, and the deposits you see may be from incomplete rinsing of the cleaning chemicals.

If, on the other hand, the water is 15 MicroSiemens (this is 0.067 Meg-Ohm-cm) you would have 5-10 mg/L of dissolved solids and a slight visible residue is a possibility. Whether or not this is caused by hardness is another question. Water without any hardness at all can still leave a residue of sodium or other salts,but these residues are softer and more easily wiped off than hardness spots.

Lyle Kirman
consultant - Cleveland Heights, Ohio
2004

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March 12, 2009

I am having a similar condition with hardness build-up on my glass bulb.
The DI water that I use is usually between 1& 3 MicroSiemens resistivity. Is that a good reason why I am seeing this build-up around my glass bulb. The DI water is usually heated to 80 degrees C for about 12 hours. This build-up is not removed by wiping off. I once used C-L-R ⇦ this on eBay or Amazon [affil links] and this cleared it for sometime and the build-up came right back. Please let me know if the DI water is the likely source.
Thanks.

Vida Ohene
- Lincolnton, North Carolina