resistance of water

[Lalit]

Hi all,
How can one determine the resistance of a given sample of water ?
Can a multimeter be safely used for the purpose ?
The resistance must be varying as we increase or decrease the distance between the terminals ?
Regards,
Lalit :roll:

 

[stevez]

The conductivity/resistance of water is often used as a way of defining purity as it can be an indicator of dissolved solids, ions, etc. As I recall, the purest water had a resistance of 18 meg-ohms dropping toward zero as the water is less pure - the resistance being measured by a standard method. Water has to be really pure to get to that level and it would seem that anything else is within the range of a common meter. I would think that the electrode material, size and spacing would have some impact on the readings. You could do some research and see what standard methods are used. If it's just a relative measurement for your own purposes then try different arrangements. Get some distilled water and see what you get - then dissolve some things and see what happens - salt, baking soda, etc.

 

[kinjalgp]

I guess multimeter can't be used for this purpose directly without use of other fixtures and devices since distance between probes will also matter while meauring the resistance.

 

[seeker]

Hi all,
How can one determine the resistance of a given sample of water ?
Can a multimeter be safely used for the purpose ?
The resistance must be varying as we increase or decrease the distance between the terminals ?
Regards,
Lalit :roll:

#1 Can a multimeter be safely used for the purpose ? absolutely yes

#2 The resistance must be varying as we increase or decrease the distance between the terminals ? Yes, resistance will vary if you move the probes.

A couple of ideas, Always use the lowest current possible to avoid eloctrolysis
and use the most inert probe material you can find ( gold, nickle, stainless steel, carbon rods out of batteries, etc.) Probe metals should always be the same for + and - probes

keep the probe spacing and current flow the same between water samples
(the highest ohm reading on your meter, like 1K or 100K or 1Meg, higher the better)

Make sure containers are very clean before filling with new water sample.


Hope this helps a little, good luck on your project, let us know your results please! Tony