You can see the working of this controller explained in the lovely diagram...

Its a simple controller, which would help to turn the water pump on, when your water tank is empty, and will turn it off when the tank gets full, and will keep it turned off until the tank is empty...

Step 1: Working

The lower sensors acts as the 'J' input and the upper sensor acts as the 'K' input in the J-K flipflop...

the working of both the sensors is opposite, i.e. the upper sensor gives output 1 when the water is detected, and the lower sensor gives output 0 when the water is detected...

With this kinda sensing, we can predict the JK flipflop's output as-

when there is water on both sensors, input = 0 1, output = 0 = motor off

when water is coming down after filling up, input = 0 0, output = 0 = motor off

when water comes below the lower sensor, input = 1 0, output = 1 = motor on

when water starts rising from the lower sensor, input = 0 0, output = 1 = motor on

when there is water on both sensors, input = 0 1, output = 0 = motor off

Step 2: The Circuit

The circuit works on 12v dc power supply, which you can give from a 12v DC adapter...

The circuit is built around 3 main ICs-

LM358 - dual comparator - sensing IC

NE555 - timer ic - clock pulse generator

7473 - JK flipflop - the controller/brain

You can see the components and the connections as per given in the circuit...

The components you will need to build this circuit are -

-12v dc jack female

-1x(100uf or 200uf or 500uf or 1000uf) + 1x10uf capacitor

-7805 volt regulator + heat sink

-2x 500k potentiometer

-2x 47k ohm resistor + 2x 470 ohm resistor +1x 330 ohm + 1x 270 ohm + 1x 100ohm + 2x 10k ohm resistor

-LM358 IC + base

-LM555 IC+base

-7473 IC + base

-1x diode

-12v relay = heavy duty according to motor

-2x red led + 1x green led + 1x yellow led

-1x BC547 transistor

-12cmx12cm prefboard

-12v DC adopter

correction - the pin 2 and 6 are connected in the 555 IC in the circuit.
also do connect the Vcc and Ground of all the ICs, you will easily get the pin configuration of the ICs on google...