On Thu, 24 Mar 2005, Mike Hord wrote:

> Where I work, we have a NanoPure filtration system which
> is fed deionized water.  The little gauge for water quality is
> given in MOhms of resistance; we get worried if it drops
> below 18 MOhms.
>
> Of course, I don't know what that means- if it's a reference
> to "resistance per centimeter of a 1 cm diameter column",
> or what, but I'd imagine it's over a pretty small distance.
>
> Anyone else have any input on this?  It's a good thing for
> people like us to know more about.  Perhaps I'll do some
> experiments...

Tap water varies from more than 200kOhm to 3kOhm (1 cm between two 
plates 1cm^2 each). It is much more reliable to measure its capacitance 
(water has epsilon-r 80). Some kinds of mineral water can appear as a 
dead short in the same measuring arrangement (under 50ohms). Fortunately 
most kinds of 'dirty' water (what is likely to flood a basement) will 
read low R.

Peter
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