Building this remote water level monitor will allow you to monitor the water in your cistern without having to eyeball it.
PHOTO 1: The sensor tube you'll be submerging in your tank. PHOTO 2: Ten 220 k-ohm resistors wired in parallel. PHOTO 3: The back of the meter, wired in parallel with a zenner diode. PHOTO 4: The meter in its wall-mounted wood base.
PHOTO: T.J. BYERS
Photo and wiring schematic show how to add transistors and additional resistors to your water watcher to increase its sensitivity.
Wiring schematic and wall mount diagram for the meter.