Re: water question

From:Lee & Peggy Wenk <>

There is a NCCLS document addressing this. I'm at home, so don't
remember the exact document number. Hopefully another Histonetter will.

In general:
- Type III water = OK for washing glassware, but the final rinse must be in
the same type of water as required by NCCLS for the type of test to be run
in that glassware.

- Type II water = OK for all stains/procedures done in histology, IM, EM,
enzyme histochemistry, cytology

- Type I water = Required for Clinical chemistry, Electrophoresis,
Quantitative immunofluorescence (NOT the IgG, etc. done in histology on skin
and kidney biopsies. This is QUANTITATIVE IF).

- Special Water = may be required for cell cultures, such as those grown in
cytogenetics, where they use sterile water. There are no NCCLS or CAP
specifications for these.

Now, as for conductivity and resistivity. These are inverses of each other.
Both reflect the amount of ions in the water. The more ions there are, the
faster electricity can be conducted through the water, so the less
resistance there is. Conversely, the fewer ions there are in water, the
slower the electricity is conducted through the water, so the greater the
resistivity is.

Most of the documents talk about resistivity. However, resistivity is
difficult to measure in a hand-held unit. Most of the times, resistivity is
measured in a unit installed in the d. water line, on the wall. There are
hand-held units available, however, for conductivity. (We purchased ours
through Cole-Palmer.)

So, if you know a little physics and a little math, you can figure out
conductivity allowed from the resistivity figures provided by NCCLS.

Resistivity is measured in ohms, or in the case of water, in 1000 ohms, also
known as megaohms, often shortened to megohms (the symbol for mega looks
like a horseshoe, with the open end up. Sorry. Can't draw it on this

Conductivity is 1/resistivity (1 divided by resistivity).  So if resistivity
is 10, conductivity is 1/10 or 0.1. The unit of measure is mho (which is ohm
spelled backwards). In the case of water, the unit of measure is 1/1000 mho
or micromho, or umho (the "u" being the Greek letter "mu", as in micron).


Type III water requires greater than  0.1 megohms resistivity, the inverse
being less than 10 umhos conductivity.

Type II water (Hx, IM, etc) requires greater than 1 megohm resistivity, the
inverse being less than 1.0 umhos conductivity.

Type I water (tap) requires greater than 10 megohms resistivity, the inverse
being less than 0.1 umhos conductivity.

(Our d. water in histology comes in somewhere between 0.4 - 0.7 umhos, so we
are under the 1.0 umhos limit, so we are OK. But on occasion, we do go
higher than 1.0 umhos, usually when they are switching to the backup
deionizer to clean out the primary deionizer. We have our own built in
tell-tale system in the lab. If the silver solution on our PASM (Jones)
stain on our kidney biopsies turns black quickly, someone (read - ME!)
better check the water conductivity, even if it is between times of

Hope this covers everything you ever (?never?) wanted to know about water
quality of resistivity/conductivity.

Peggy A. Wenk, HTL(ASCP)
William Beaumont Hospital
Royal Oak, MI 48073

----- Original Message -----
From: "Garza-Williams, Sara" <>
To: <>
Sent: Monday, March 19, 2001 3:57 PM
Subject: water question

> Does any know where I can find information on conductivity of water (CAP
> question)? Specifically for good quality water for special stains, and
> immunos?  I need to know the acceptable range.
> Thanks in advance.
> Sara

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