Resistance between steel wires in water delayed response I am trying to make a wire wave gauge by measuring the resistance between two stainless steel wires. Theoretically, the output voltage reading should change the deeper the wires are in the water. If you look at the attached photo, the graph shows a nice wave when I move the gauge up and down but when I leave it stationary in the water the signal decreases very very slowly. I am hoping someone with very specific knowledge can shed some light on why this is happening. I need to have repeatability with this test and make a calibration curve of various depths and I can't really do it if there isn't a clear voltage value for each depth.
 A: To measure resistance, your multimeter injects a small amount of precisely-known current through the circuit and measures the resulting voltage, then converts this to a resistance reading. In the absence of stirring action in the water, that current flow is probably electrochemically growing a (very thin) chemical layer on the surface of one of your electrodes which affects the transport of electrons or ions through it, or disassembling the native chromium oxide that normally coats stainless steel parts when immersed in water. 
Many sorts of stainless steels are available. If you are using 304, try switching to 316 instead, or another grade that is specifically intended for use in salty and slightly acidic conditions. 
Try manually adjusting the range of the metering device to a higher resistance setting, as this will reduce the injection current and slow down the formation or degradation of that film. this will require you to choose a more sensitive detection range, which might degrade your signal-to-noise ratio. 
Also note that in general, electrochemical cells like this are notoriously affected by the amount of stirring action, which is going to make life hard for you. 
A: Other answers are really good. I would only suggest you have two meters, one inside an enclosure with a small hole at the bottom, so water would flow in and out slowly.

Then look at the difference between the two meters.
