I make this circuit using two transistor 2n2222a and 2n2907. Which output terminal is connected with the relays anther terminal.  When the water tank is properly filled then both tansistor input will be 1 then the output of those is 0 and the relay turned on. And motor will turned off. And when upper part of the water tank is become empty then the transistor Q1s input is 0 and at that time the water is present at the lower level of the water tank then transistor Q2s  input is 1 and output of the two transistor is combined and keep relay on and motor remain turned off. The motor will remain turned off until the water of the tank is completely empty the two transistor input in going low (0). When the input of the two transistor input is 0 then the combined output of the two transistor is 1 and the relay turned off and the motor is turned on. And the process is repeated.
Basically in this circuit two transistor s  are works different according to their input signal. So, there are two type of modes are applicable in this circuit.