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DI Water Standard

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Is there a standard to define what "good quality" DI water is. What is the maximum conductivity that should be allowed? less than 5 micromhos/cm, less than 10? All thoughts and opinions will be appreciated.

Kurt Sammons
high performance conductors - Inman, South Carolina

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I think you're going to get lots of opinions on this, here's mine for what it's worth, I'll let my tank go to 100ppm, but no higher. I've been in clean rooms that run their tanks at 5ppm. Most of the system suppliers guarantee <5ppm coming out of the resin tanks. It's really up to you to set your own standard based on testing you're own product(salt spray, various adhesion test, etc,...)

Sheldon Taylor    supply chain electronics Wake Forest, North Carolina

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"There's nothing either good nor bad but thinking makes it so." --- Hamlet.
Think about the sensitivity of your application to contamination.

'Good quality DI water' is perhaps 18 Meg(a)ohm-cm water from mixed bed polishing. See Type I Reagent Water requirements in ASTM D1193 [link is to spec at TechStreet]. Maximum conductivity of 0.056 microSiemens/cm,* max. chloride 1 ppb, max. silica 3 ppb, max. organics 50 ppb.

*Siemen (S) = mho = 1/ohm
For most natural waters, conductivity in microSiemens/cm x 0.55 to 0.70 = ppm TDS.

Ken Vlach - Goleta, California

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There are actually four grades of DI water in the ASTM standards literature: Types I, II, III and IV. These are actually pretty good benchmarks.

A water handbook should list these and other standards, but there seems to be little consensus in industry over a quntitative definition of "deionized water".

Many customers specify the resistivity or conductivity of the water used for final rinsing, and many process chemistry suppliers also have specifications for water used in their processes. For example, it is not unusual to see specifications for water with a resistivity of > 2 Meg-Ohm-cm in the mirror manufacturing industry, and > 3 Meg-Ohm-cm in the electronics plating industry.

Lyle Kirman
water treatment systems - Cleveland, Ohio