Here is an extremely simple circuit to check the water level of your tank. It works on the principle that water is a fairly good conductor of electricity.

The 9v supply can be given from a battery and a buzzer can be used as a source of indication.
The 9V battery and the buzzer together cost Rs20/- or 50 cents. i bought 20 meters of wire to make the connections to my room.

The circuit diagram is as shown below:


When you apply a voltage preferably 9V so that it can pass through the water even if the water's conductivity in your area is low. The circuit is completed by the rising water and the buzzer starts beeping loudly

you could add a 555 timer to the circuit to get a series of pulses instead of a single long buzz.

happy water saving