pwillard:
Water conducts based in the impurities in it so I would expect the numbers to vary greatly depending on your source of water.I don't think you are doing anything "wrong".
Ultrapure water is hardly conductive at all while seawater approaches the conductivity of stainless steel (which really all that conductive compared to say silver wire.)
Interestingly,
so how could I create a rule percentage, regardless of the soil,
able to tell if it's humid 80%, for example?