1 Water Level Indicator Circuit

This water level indicator is very easy to build and does not require any good background in electrical engineering. It is very similar to 555 IC based water level indicator, but much simpler to construct.

Water level indicator schematic

Part list:
R - 390 ohms (4pcs)
Rb - 22k ohms (4pcs)
Q - 2N2222 or any  general purpose NPN transistor (4pcs)
LED - red, green, yellow, orange or similar (but not a  high intensity or power LED) (4pcs)
9V battery
piezo buzzer 6V (optional)
220 resistor (optional)

Operation:

water vs air resistance in 1 inch gap

Lets look at the diagram above. Assuming that the resistance of air is around 10^8 to 10^9 ohms-meters and water resistance is around 182 kilo ohms-meters. For 1 inch plate gap, air resistance is around 3Meg  while water is around 4.62k. It is clear that the transistor and LED is turn on only when the plate is wet. Just place the plate 1 at the lower part of the water vessel or tank and plate 4 at the top most level. You can add a buzzer in parallel to any indicator to alarm you  on the water level. See diagram below.

Buzzer add-on