Hi, I am trying to build a conductivity meter as part of a school project (I have to measure the conductivity, among other things, of local water systems). Unfortunately, I cannot buy one for this project, as it should be home-made for these purposes. If I wanted to create a meter that actually quantitatively measures the conductivity of water samples, would there be a way to create one at home using supplies from hardware stores? Or, would I simply have to buy one to get an actual qualitative reading and not have to guess conductivity based on how bright the bulb on my crude home-made one is? If there is no short way, how best might I go about measuring conductivity with a simple light-bulb based meter where I judge conductivity based on how bright the bulb is? Also, if I had to use a light bulb, what would be the maximum voltage I could put on the bulb, since using say a 9v battery would most definitely blow a 2.4v bulb from a flashlight? Is there a definite ratio between recommended voltage and maximum safe voltage?