Here is a simple circuit for controlling water level in the over head tanks. The unit switches off the pump when the water level reaches a particular level, sensed by a simple water sensor.

The switches are provided to manually switch on or off the water pump. Two LEDs indicate whether the pump is on or off.

The sensor is not crical. You can make one using a two pin electrical plug. 

The unit housing is made of flex board, 4mm thick. It is easy to cut & drill. Various panels of the box can glued together with quick drying glue or assembled together using a stapler gun.

Standard sealed 2-pin power plug can be used as water sensor. Ensure that the plug is properly sealed; put epoxy if needed.