Water tank overflow liquid level sensor alarm circuit

Water tank overflow liquid level sensor alarm circuit is a simple electronics project for school students. In the previous articles we had discussed about numeric water level indicator and water level controller circuit ,but those circuits are much complex and are advanced projects for engineering students. The circuit schematic for water tank over flow alarm is shown below. It produces a beep sound when the water tank  is completely filled by water.The advantage of this project circuit is that it saves water from accidental over flow. The circuit simply consists of a liquid (water) level sensor or water level detector with BC547 transistors. Any electronics hobbyist can implement this circuit at your home or work places at a cheap rate ($0.5). The heart of this water over flow circuit is  the transistor switching part. So this circuit always prevents the wastage of water when you forget to switch OFF the motor pump set after switch ON.

Circuit Diagram of water tank level alarm

Water tank overflow alarm circuit

Components required

  1. Power supply
  2. Resistors ¼ Watt (1kΩ x1, 100Ω x2)
  3. Transistors (BC 547 x 2)
  4. 6V Buzzer


  • Water over flow from a tank or reservoir is detected using this simple project circuit. Firstly close the switch SW to turn ON the device.
  • Initially the potential at point A in the circuit is Vcc, so the transistor Q1 remains in ON state (Read transistor act as a digital switch) and its collector voltage at Vce sat (0.02V).
  • The collector voltage of Q1 is fed to the base terminal of transistor Q2 via100Ω resistor.
  • 0.02V is not sufficient to turn ON the transistor Q2, hence it remains in OFF state and the buzzer will not produce any sound.
  • A connection from ground is dipped in the water reservoir. When water level rises, the ground comes in contact with the base terminal of transistor Q1. Thus it changes to OFF state and the collector voltage rises to Vcc.
  • The high voltage at the collector of Q1 turns ON the transistor Q2 since this high voltage is connected to the base of transistor Q2, then a current flow occur though the buzzer circuit and it produces beep alarm sound. (Read transistor act as a load switch)
  • See the simulation window below, here instead of buzzer circuit we have used a LED for simulation. The switch ON is similar to water touching the point A.
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Simulation of water tank level sensor alarm

BC 547 transistor pin out

BC 547 transistor pinout

50 thoughts on “Water tank overflow liquid level sensor alarm circuit

  1. as per given above the circuit of water tank over flow ,i made it but its not working in the water ,can u please help me to how to worked proper

  2. sir this project is not working please tell me how to check weather circuit is correct or not .
    when i touch both wire bellow and above in the water bugger rings please reply soon.

  3. This circuit works, however the sensor does not. The resistor above point A drops the voltage at point A to around 1 volt. This is insufficient voltage to conduct through the water. If the lead from point A is grounded, the circuit works fine. However placing the two leads in the water does nothing.

  4. I am a learner in this field though I am Electrical engineer I never worked with electricity but work on chemical plant setting and turnkey project. I am 76 years old and have keen interst in this field will you help me .If you send me the emil I will feel that you have noted my wish and give me reply

    Regards Ramesh K Phadke

  5. He I sir circuit is not working wen the two leads of water tank touch together buzer rings but in the water not working kindly give replay

  6. please send simulation execution clearly and are we use 3 led lights in this simulation.and tell simulation results in matlab please please

  7. great. But with this the dc current pass through water which causes lose of energy and ionise the water. Can u give me idea in which the current do not pass through directly water.

    • deepak, you might want to consider switching up your sensor. If you don’t want any current running through your water, you could try a relay based on a float system. An example of this can be seen in a toilet. When a pump brings the water to a certain level, the float will signal to shut it off. Another option would be creating a capacitively based sensor. It appears to be fully insulated, so no voltage would pass into the water. Another type of sensor would be resistively based, although I’m not sure if that would prevent electricity from going into the water. Hope this helps

  8. in this project how you connected alarm and controller as same time may be the user of this device u
    se other water tanks ? second question how you use two circuit one is push water from tank controller and the other fill the water to the tanks automatically? thanks!

  9. hi,
    I tried using 2amp but still its not working in water, at the same time when I connect both the probes directly it is working. please suggest soon.

  10. Can you please explain the other reasons of water flow like heavy rain,floods etc.
    Explain the project with theory for class 6th
    The project name is water level alarm.

  11. hi sir,
    I am Naveen. I need to do a small project to avoid over flow of water from tank.
    conditions for that project:
    from motor water is feeding to an vehicle which as an 500 litre tank. if the tank filled immediately the motor should be off automatically or the valve should close automatically.
    kindly give an idea to do an autamatic system.

    • automatic control with motor on and off, once tank full automatic off and its empty automatic on,,,,,,,,,,,,,for more details contact me

  12. Sir, please let me know can the same project with the same components can be implemented in home where we will have 240W power supply?

  13. I Have tried your system but on short circuiting it works but not in water thought I am using a 5amp 6 volt dc supply pl suggest nor with grounding

  14. sir I work when vcc connect to ground. the water has very high resistance approx 1megaohm I try to connect direct 220v by rectifie by 1apm transformer but I will not work

  15. Hear the resistance of water is very high 1gegaohm approx so 1apm transformer does not work I tried this I check the amp of circuit is very low approx 1 micro amp .

  16. Hi Sir,

    I am studying in class 11. This water overflow alarm belongs to 11th standard or not. If not, then please suggest me some more ideas, so that l won the district working science models exhibition. Please reply me ASAP.

    Thanks & regards
    Aditya Aggarwal

  17. Hiii.
    Dear sir .
    Problem is that we are not getting high level alarm.
    Low level alarm is working .
    What i shiuld do…

  18. Hiiii

    High level water alarm not working ..how i shold be cheak . How shoukd be repair it…
    Pls inform me any budy….

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