yes, because thats exactly what an electronic ppm meter does; pure, lab grade distilled h2o is an insulator, in other words it cannot conduct electricity. add a few dissolved salts and suddenly it becomes conductive. (salts are metalic) as more salts are added to the solution, the conductivity increases, the resistance is lowered, and the water becomes more conductive. so the higher the ppm, the lower the resistance.
that makes it sound pretty simple right?
unfortunatly its not.... 2 reasons why:
1 your average contractor grade multimeter is not built with a low enough scale to be able to make accurate measurements. and since a digital multimeter uses true RMS (root, mean, square) math functions to give readings, it is not the ideal instrument of choice. you would need an analog meter, like an old simpson, that has been calibrated by an expert.
2 there are so many minute variables in a procedure like this it would be almost impossible to take two identical readings off the same sample... the positioning, depth and distance between the electrodes will greatly affect the readings, as will many other factors such as contaminated samples(even the oils from a single fingerprint would mess up your reading by at least an order of magnitude), weak batteries(in the meter), lack of a known control to compare results against, and many many other things.
so to answer your question, is it possible?
yes
is it practical?
not at all. ppm meters overcome most of the problems by applied engineering, product testing, more engineering, etc etc. its why they cost what they do for something so simple: consistancy.
to use a multimeter to get consistant, accurate measurements would take a lab setting using scientific method. to much of a pain in the ass IMO
