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Municipal Water Supply Sensor Controller Circuit

Municipal Water Supply Sensor Controller Circuit

The post explains a simple water sensor with pump starter circuit for switching a pump motor during municipal water supply periods. The idea was requested by Mr. Hitesh Thapa.

Technical Specifications

Is it possible to make a automatic water pump starter which turns On only when the city supply line has water flowing.

Here is the scenario.

- City Supply Line opens only for 1 hour anytime during 6AM - 10AM or rarely sometimes in the evening depending on the water guy.

- We need to keep a watch during these times and keep the main tap open to see if the water has come.

- Once the water has come, we turn on the water pump attached to the main supply line to pump water into our underground water tank.

Could this be automated, like we install some sensor between the water pump and the main supply line that detects water and turns on the motor only when the supply is in full flow?

I have made the water level indicator at home from watching some videos online and it works fine for the overhead tank at home but this one seems to be tough nut to crack :).

Any help is highly appropriated.

Hitesh Thappa

Circuit Diagram

The Design

The circuit design of the proposed municipal water sensor with pump starter is very simple as may be witnessed in the shown diagram.

A Darlington TIP 122 transistor becomes the main active sensing device in the circuit. The device being a Darlington is very sensitive and thus becomes specifically suited to the application.

Its base and the positive DC are together clamped as probes across the water pipe mouth where the incoming utility water is intended to be sensed.

In absence of water the probes stay separated with air gap which renders a very high resistance across the probes which in turn keeps the transistor/relay stage switched off.

The 10uF capacitor at the base of the transistor ensures that the transistor does not get rattled or disturbed by external noises trying to make way through the sensor wires.

When utility water supply initiates, the pipe mouth begins throwing water into the adjoining tank, the speed of the water through pipe brushes across the probes creating a relatively low resistance across it.

This low resistance allows the positive DC to reach the base of the BJT triggering it into conduction...the transistor now conducts and switches ON the relay, the relay contacts shift position and switch ON the connected pump.

Upgrading the above municipal water sensor into an overhead tank overflow cut off circuit

The discussed circuit in the above section can be appropriately enhanced with an additional feature which will enable the circuit to sense an overhead tank full situation and switch OFF the relay along with the pump motor. The upgraded circuit design can be viewed  below:


About the Author

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials. If you have any circuit related query, you may interact through comments, I'll be most happy to help!

56 thoughts on “Municipal Water Supply Sensor Controller Circuit”

  1. Thanks sir,
    But I have one another problem.
    Relay on without water in pipe line.
    I put two probes across the water pipe with 1 pair of wire. 1 wire has dc voltege of 5.35 volt which comes from this circuit and the pararrel wire which is connected to bais of transistor also has dc voltage of 4.80 volt so how is it posible? And there is no water in the municipal pipe line even relay on !!! And there is 2 cm distance between two probe and also no continuity in wire while no water in pipe line

    • Hi Deepak, it could mean either your transistor is faulty or its ground connection is broken. Change the transistor and check again. Also preferably connect the base wire through a diode to eliminate confusions.

  2. Hello sir,
    As it used 10uf 25 v capacitor in the base of transistor after the resister 1k. wht will happen when capacitor is charged and no water in pipe line than capacitor produce voltage to base of transistor without resister so it will not harm the transistor ?
    As we know base of transistor need less than 0.7 v.

    • Hello Deepak, the charge stored in the capacitor will be restricted to a level which is perfectly safe for the transistor base. In fact the voltage level inside the capacitor will be restricted to 0.6V or 0.7V, because the forward voltage drop of most BJTs is restricted to this value therefore the capacitor can charge only upto this limit, so nothing to worry..

  3. Hi Swagatam,
    The circuit is working fine. Request you to suggest a suitable modified circuit for eliminating the problem of pump frequently switching on off frequently during the starting few minutes of water supply. I wish once the pump is started should not go off for a couple of minutes even if the sensor are sensing water and air in sequence until the supply is stable.
    Hope I am clear.
    Thanks in advance.

    • Hi Imtiyaz, I am glad it is working for you!

      To solve this you can add a 470uF/25V capacitor across the relay coil, this will make sure that the relay does not stutter during the initial fluctuating water supply conditions.

      • The shuttering still persist, without resolving continuous practical application is not possible.
        As I am a mechanical engineer, request you to forward a complete circuit with discussed modification and introduction of selector switch for auto and manual selection. It would be more asthetic if led indicators are also introduced.
        My e-mail id is
        Thank you

        • Hi, did you connect the capacitor across the relay coil? Even after you connect it if the water supply is too much fluctuating with large delays between ON and OFF then the relay will stutter,and cannot be solved with the above simple circuit.

          In that case you will have to build a IC 555 monostable circuit and use it.

          build the circuit which is shown in the following article


          remove the piezo, and connect the two wires with the water pipe probes.

          remove the LED, resistor, and replace it with a relay, make sure to connect a diode across the relay coil.

          The 1M pot will need to be correctly adjusted such that the stuttering just stops.

          • Thanks for the guidance,
            All the 3 parts are working
            A)Water sensing to start pump
            B)Time delay to stop shuttering
            C)Overflow pump stopping

            Now one small problem, when incoming water stopped#pump goes off
            But a slight residue water in the pipe touches the sensor the pump is restarted, how can this issue be tackled?

            • That’s great! I am glad it’s serving the purpose for you.

              To solve the present issue, You will have to position the sensor in such a way that the water touches the sensor only when there’s some force in the water, otherwise without any force the residual water should be unable to come in contact with the sensor points.

  4. Is it not possible to use 12v AC instead of 12v DC ? A transformer could be used to convert 220v AC into 12v AC ?

  5. thank you sir for ur kind advice one more query how much should be the gap need to maintain between the sensor probes and voltage to supply ( our supply pipe is 1.5 inch dia )


    • the distance could be around 1cm, but make sure that it is built in such a way that water does not clog between this gap when water supply has stopped.

      • Hi, Tx for the relief you are giving so many people.
        I have a request if you could give me a simplified complete circuit diagram including the non stuttering on/off at low supply for upto 1hp pump.
        Will be greatly obliged . Thanks

        • Hi, thanks, to prevent stuttering of the relay, you can simply add a 1000uF capacitor right across the relay coil.

  6. good day sir
    is it possible to use probe be made off aluminium ( easily avaliable from home utensil) instead of brass ( not easily availiable in my place )


    • good day john,

      you can try the same circuit which is explained above, for indication you can connect an LED in series with the base of the transistor.

      for the sensor aluminum will work but aluminum may be also prone to oxidation. instead you can use copper and tin it with a thick layer of solder…the solder should be of the highest grade with a tin/lead ratio of 60/40…or better.

  7. good day sir

    i need acircuit which detects water flow and giving indication of same when pump starting to fill the overhead tank . we are using pvc pipes and what kind of snsor probs can be used instead of brass for effctive response


  8. I want to buy a 'READY TO USE' Controller
    which can Switch – On the pump, when it detects
    water flow from the City's supply and when
    the same stops, it Switch – Off the pump. Has
    any company incorporate this circuit design in
    their Controller device ? And if so, please list
    the name and contact info. Thanks

    Gurgaon HR

    April 27, 2017

    Note: Needless to say, the controller, should have
    other features, like Switch Off the pump, when tank
    gets filled

    • Ganesh, the concept explained is very straightforward and should work without fail, you might have done something incorrect in your design…

      you can confirm the results using a cup of water and immerse the sensor points inside it to check whether the relay clicks or not…

  9. How should I make water level controller system in this same circuit? So that after filling tank the motor will automatically turn-off, please guide me.

  10. As you said I purchased 3 pole relay of PLA company (3C/O MPC 12D-5) having 11 pin encircled. It has 3 pole so on 3 common , 3 N/C and 3 N/O. Now how should I make a connection of 3 phase motor with this relay? please help me out.

  11. Finally I got circuit diagram from Google images, Mr. Swagatam Majumdar can you tell me how much voltages is required to run this circuit because i'm mechanical student I've not enough knowledge about electronics circuit.

    • Faisal, you can operate it with 12V… if the relay is also 12V rated, or any voltage that matches the relay coil voltage

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