Simple Water Level Indicator

There is always a problem in our home whenever we switch on the motor and forget to switch it off, after the tank was filled with water and spilled out. So much of water and power is wasted. So, we have decided to solve the problem by making a simple circuit with transistors and a Buzzer.
              Let us find out the resistance of our tank water which about 53.7K which is very high.

             so we have used a transistor(bc547) for the purpose of amplification in CE mode with beta 110 ~ 220 which may not sufficient for the buzzer to drive directly. So we are using another BJT for switching. The configuration is in the form of a standard Darlington pair, which increases its current amplification capacity hugely.The current through buzzer is          β(β+1)I_b(Q1)

                       The purpose of Resistor and Capacitor is to insert some delay so that the transistor  is on for some time (R*C=2.2mS) and so the Piezo Buzzer starts ringing. The whole circuit is given 9V D.C power supply. I have used a 9V battery