I'm thinking that it'd be good information to have to know if the submarine springs a leak. To that purpose, I'm going to setup three water sensors.
I started off looking at the directions found here:
However, the schematic says any NPN transistor, but I think they must have different activation voltages. After trying two different type of resistors (not the ones listed), I bought a 2N4401. I modified the circuit by reversing the voltage and removing the LED; so that transistor emitter feed would be feeding voltage to an analogue pin on the arduino. I also used a 100k trim-pot.