I think your measurement instrument is fine. What is not is your understanding of resistance: there is nothing like this "resistance of water". In your case, the measured resistance depends on the distance between the immersed probes. The relevant concept is "electrical resistivity" or "volume resistivity" of materials (see Wikipedia). For example, if a 1m x 1m x 1m solid cube of material has sheet contacts on two opposite faces, and the resistance between these contacts is 1 Ω, then a right 1m x 1m x 2m parallelotop will have a resistance of 2 Ω.

Now, usually, the resistivity of water is high, and depends, as you know, upon the concentration of minerals it contains (or more precisely and generally, upon the concentration of ions). Pure water is a relatively good dielectric, but still far from being as good as plastics because there is always a small percentage of ions inside water (google "ph of water").

So, often, water will not cause short circuit in A4 battery powered instruments or so. Still, as electronic components are often very sensitive, even very small amount of currents may cause important failures (think about op-amps that have usually input current in the nA or pA ranges). Furthermore, since we usually ignore the concentration of minerals, it is evident that these instruments shouldn't be immersed inside water. Furthermore, water causes other problems like oxidation etc.

Now, for high voltage powered circuit, working, e.g., on the 220V main, even 20 kΩ gives about 10 mA of current, at which the heart begins to fibrillate.

In conclusion, water is really undesirable in electrical circuits.

posted over 3 years ago

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3y ago

coquelicot‭

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