I know that in the navy we used demineralized water to pump through the mainframes. If all the minerals are removed, pure H2O is not conductive. So I would think that the more minerals are present, the more conductive it gets.
Conductivity is not very good for nutrient replacement, I'd considered it at one point.
Problem is: as the plants uptake nutrients, they expel counter ions (K+,H+'s etc) and the conductivity is typically the same in the water, but does change very close to the plant's surface as the uptake takes place.
If the plants did not do anything to the water, then yes, you might generalize it to some degree.
With hydroponics, as the solution becomes very concentrated, then it becomes more of a problem and Conduct meters are useful.
But we cannot tolerant that type of sludge in our tanks