Hy, This is one of my favourite projects because it is easy to make and needs a very few things. Mind it that I have not Invented it. Just made it by the help of other websites. As the current from the electrodes flow to each other through water and earth is provided the transistor gets charged and turns the led or the buzzer or whatever you have attached. I hope you like it.
Step 1: Supplies
Transistor BC 547 (2)
Resistors :- 1k, 470 KR
Step 2: Building
Firstly attach BC 547 any side of breadboard as you see in the picture.
Now attach the 1k resistor from the middle leg of the transistor to the GND side.
Attach the jumper wires from the leg of the transistor to the GND side.
Attach the 470KR resistor one pin down one pin right from transistor leg which will be use to reduce the current of buzzer and led.
Now attach the buzzer positive at the resistors leg and negative at the transistors leg line.
Now attach to wires in the same line you placed the buzzer if you want to put led. If no then follow the next steps. In this step you just have to make two terminal as I did to use both led and buzzer.
Now the final step take a jar and stick the electrotodes at the upper level or at any level you want. And attach the other two ends at the bread boards at the middle of the transistors leg line. Now you are done power it and tattatattta. You have successfully made a water level indicator, you can place it in your tank at your homes when the water will touch the electrodotes the buzzer will beep and led will be lit if you have done the setting of led. You can modify it and make two circuits on this breadboard, both will be same but place the other twol wires at the middle level which will show that the water reached the middle level.