Water level controller circuit described here control the water level inside a tank. There two modes available with this water level controller circuit. The first mode is empty mode, when the controller will drain the tank if the water level reach the upper limit, the pump will be used to suck the water from the tank until the water level drop below the lower level. The second mode of this water level controller is fill mode. Here the pump will be used to fill the tank with the water when the water level is drop below the lower limit, the pump will be activated until the water level reach the upper limit. Here is the schematgic diagram of the water level controller circuit:

water pump controller circuit schematic

The circuit uses NOR logic gates, only one IC package and one transistor is needed for the active components, very simple design. The default position of  SW1 (as shown in the schematic diagram) is empty mode, just switch to other position to make the water level controller works in fill mode operation.  The relay can be used to control almost any type of water pump motors. Please be aware that this circuit works only with water or other electrically conductive liquids.