Introduction: Simple Water Sensor

Picture of Simple Water Sensor

I will Teach you how to make a simple water sensor circuit

Step 1: Gather Parts

Picture of Gather Parts

Parts List
1 General Purpose NPN Transistor $0.10
1 50K Trimpot $0.15
1 47ohm Resistor $0.01
1 LED $0.08
1 Proto Board or You can etch A PCB
1 3 volt power source battery, wall wart, whatever

Step 2: Learn the Layout

Picture of Learn the Layout

[Play Video]

Read Circuit Diagram

Step 3: Create PCB (skip Step If Using Proto Board)

Picture of Create PCB (skip Step If Using Proto Board)

The Schematic is made with ExpressPCB which is a free PCB Layout Software you can download it here
Than Download the PCB file and open and print it and make your PCB. Here are a few links to Instructibles that show you how to make a PCB
water sensor.pcb is 3v
water sensor2.pcb is 12v
these PCB schematics are free to use if I see them being sold buy anyone but me you will be contacted
Cheap and Easy Toner Transfer for PCB Making
The Saltwater etch process

Step 4: Build It

Picture of Build It

Build time will update once I make the PCB

Step 5: Connect to HHO Cell or Any Other Water Sening Probe

Picture of Connect to HHO Cell or Any Other Water Sening Probe

Here are some mock ups of how to connect it to a HHO Cell or just detect water.


Picture of 12 VOLT CIRCUIT

Here is how to setup the circuit to run on 12 volts from a car battery the circuit is still the same just some resistors are added to the probes to protect the transistor and a larger resistor to protect the LED


DaveJ96 (author)2017-10-11

Really like this and mr_man's comments are great too. What I am hoping to do is to but a system to check 5 separate points in the house for leaks, and have a small board on the wall with a red and amber led for each location a green system light and run through a raspberry pi or arduino uno. The idea being that for each location if it is leaking at the time the red led is lit, if it has leaked but is not now, then the amber light is lit. The green system light will be lit if the system is running and there has been no leak at any point since last reset. A button to reset the system on the board would be good too. I can do the programming either Arduino or Raspberry pi but the electronics are eluding me. ideally would be a 3v3 system for the raspberry pi without doing voltage changes and also taking into account the points raised by mr_man. Any help would be much appreciated.

T448 (author)2017-01-31

Any ideas why my LED would remain on all the time regardless of the moisture on the sensor? What have I done wrong?? Driving me nuts! Thanks

DavyZ (author)2015-12-25

how do you prevent corrosion on the wires? I want to use it in the ocean and corrosion will be a problem.

Cyberscann54 (author)DavyZ2016-12-08

I just was looking over the comments and the pencil leads are a good idea but brittle get some cheap heavy-duty batteries AAA to D no 9V they have carbon rod's in them and are not dangerous to disassemble the don't corrode or rust and are conductive and really cheap if you are in the USA you can get 8 AAA OR AA for a $1 at most $1 stores

vamsikurre (author)DavyZ2016-01-07

Even I have similar plan and did some reading about "Electrolytic corrosion" and found out that inert metals like platinum or gold dose not corrode. but they are a bit expensive for me :) So I am planning to use a good stainless steel rod's as probs as they corrode and eaten away very slowly compared to copper and aluminium. I think graphite (pencil lead) also makes good electrode.

Cyberscann54 (author)vamsikurre2016-02-26

an option would be to use gold electrodes

MG17 (author)vamsikurre2016-02-26

If you're doing this for drinking water DON'T USE STAINLESS STEEL !!!

I was going down that path too, thinking that there will be little/no corrosion, but then I noticed a strange substance in the water. Turns out that using stainless steel as electrodes is a bad idea as it releases a poisonous substance! ...


TibiA1 (author)DavyZ2016-01-13

look for stainless steel wire used for welding and use terminal board for conexion

cihanc1 (author)2016-09-28

Hi. I need to use this with raspberry pi. Raspi pins operate in 0 - 3.3v. so which
resistor value do i need. I ask if i have to change 47 ohm R. Then i willl
connect raspi pins to where the led is and then read value with wiringpi functions. Right? Thanx

Cyberscann54 (author)cihanc12016-12-08

if you are going to use this with a raspberry pi you will use the 3v circuit without the LED and 47ohm resistor or you can keep it as is with the LED and resistor. if the pi is powering the circuit you can attach a wire between the collector of the transistor and the LED and put it on one of the input pins and you can put a resistor in the input wire to ensure the maximum current going to the IO pin don't exceed 16mA

NealP5 (author)2016-08-03

How would I modify this to "press" a button instead of the led? I am considering coupling this with a dash button for an ultra cheap smart sensor! So how would I make this activate the button?

Cyberscann54 (author)NealP52016-08-16

To better help you what does the button do. What does it turn on or off. Is it in series(a switch wired in line with the + or -) with a pump is it a button of a control board(circuit board). Depending on this it could be as simple as an other transistor or a Mosfet transistor (can handle more power) or a relay switch (a lot more power)?

NealP5 (author)Cyberscann542016-08-24

I'm filling 5 gallon bottles with a slow 50GPD reverse osmosis system in a kitchen that is 100 degrees most of the time. I want to have it notify me when the bottle is almost full as I have forgotten and flooded the damn kitchen 3 times now.

NealP5 (author)Cyberscann542016-08-16

it's just on a tiny circuit board. It's the button on the Amazon Dash Button. I wanted to make this as cheap as possible and these sell for only 5 bucks.

Cyberscann54 (author)NealP52016-08-24

so is the button to be activated when a liquid product gets low if so this sensor circuit won't work. what is the dash button doing ordering a product or some modified use i will create a circuit to fit your needs to work with the button

fthebunny1 (author)NealP52016-08-23

A pull up resistance would made the job. It's very simple : electricity is lazy, really lazy, so it will always take the shorter, easier path. A resistor is a kind of hill, so it is harder to take, than a wire, which is a flat, right lane. A pull up resistance, makes the path to the Vcc, harder to reach, than GND. So it keeps your input to GND. But if you cut the wire, the electricity will pass by the resistance, and give a HIGH state to your input on your dash button.

Now, if you need it to be a short impulse, not a continue one, you must look about the 555, the most famous timer of all time. It will create the impulse, once, even if it still high at its input.

fthebunny1 (author)2016-08-23

Great project ! I was seeking something like this since a while, but just found the good search terms now ^^.

I have a question, does this :

Wouldn't be cheapest ?

MuhammadN104 (author)2016-03-05


EmerSonE3 (author)2016-01-23

Can you show me the diagram in PCB ?

aphy101 (author)2015-11-10

Hi we are planning to use this circuit in our project but how do we calibrate it?

Cyberscann54 (author)aphy1012015-11-23

adjust the variable resistor to calibrate

MG17 (author)2015-10-11

Thanks for the tutorial. I's helping me make automatic watering bowls for the dog and cats.

I got it working with the LED, but I can't get the arduino to read the on/off. I tried connecting wires where the LED should be to a digital pin with DigitalRead, and an analog pin with AnalogRead, but can't read any sort of signal.

Any ideas on how to interface this with an arduino?

syedumarjunaid (author)MG172015-10-18

try connecting 220 ohm resistor between emitter and ground and connect arduino pin between emitter and resistor then see if you can sense any voltage

MG17 (author)syedumarjunaid2015-10-18

Thanks for the reply. For anyone else wanting to detect water with arduino - turns out that you just need to connect a 10k resister between 5v and A0, then connect the probes to A0 and GND. Works like a charm :)

Great circuit/tutorial though, I'm sure I'll find a use for it outside of my aurduino project

MG17 (author)syedumarjunaid2015-10-18

Thanks for the reply. For anyone else wanting to detect water with arduino - turns out that you just need to connect a 10k resister between 5v and A0, then connect the probes to A0 and GND. Works like a charm :)

Great circuit/tutorial though, I'm sure I'll find a use for it outside of my aurduino project

vederstein made it! (author)2015-07-25

I put a dpdt 12vdc relay in place of the LED. Now I can control the water level on my model steam boiler.

It was a pain though. The documentation I had on the transisistor had me wire it backwards. Also, the power supply I was using was way too noisy. After taking the battery out of my classic car, it worked.

FYI: Don't use an autmotive battery charger as a steady power supply.

vederstein (author)2015-07-25

Miken8 (author)2015-05-23

Just wondering how I could make a very simple sensor to detect when something is no longer in water. So when the water sensor is no longer active it will alarm with a small speaker/beeper. I want to make something to put in a float used for crab pots so if a would be thief attempts to remove it the speaker is activated. Hopefully something low voltage. This would be in salt water if that makes any difference

TomHoag (author)2015-02-06

It is simple and very effective! Note that the circuit response will vary depending on the medium such as fresh water, lake water, salt water, etc.

Wayne TheS (author)2014-10-01

Thanks....the video saved me from pulling my hair out. Was not aware in re: tying the pot half to ground. I intend to use this as an auto switch on my bilge pump. I intend to add a three way switch, Off, Auto, Manual. I assume I will need to amp up the output to pull in a micro relay? If I am not mistaken the relay will require about 60 ua ....have not gotten it in yet to see. Any suggestions? Thanks for a great vid.

Cyberscann54 (author)Wayne TheS2014-10-02

I could see replacing the LED with a relay most relays are designed to operate from low voltage sources and switch on or off a high voltage supply so just remove the LED and its resistor and put a relay in there place and I'm guessing this is for a boat so powering it should be easy with no changes to the circuit since boats use a 12v system the circuit was designed for 12v you just need a 12v relay that can handle the pump. Thank you for the comments and good luck.

Wayne TheS (author)Cyberscann542014-10-02

Thanks for the info...For anyone else interested, I will also be including a delay off timer of 10 secs or so in order for the water level to fall well below the probes and prevent an On/Off/On/Off scenario from wave action etc. The probes will be mounted about a 1/4" above the highest point of intake of the pump...this should allow the pump time to lower the level to the point of cavitation and then shut off....leaving the probes well out of the water.

Cyberscann54 (author)Wayne TheS2014-10-03

well since you want a delay timer a 555 or 556 chip can be used and the sensor can also be built from it if you want I can design the circuit for you and all you will need to do is get the parts and build it just let me know if you want me to do it

Hi, did you post the circuit as described above (ie to prevent on/off/on) using 555 timer etc?

Wayne TheS (author)Cyberscann542014-10-03

That would be great! Keep in mind that I am new to electronics (66 yrs old) so I do well with pictures :) I have plenty of 555 and 556's as well as ATTiny 13 and 85's as well. I have managed to struggle through burning the Tiny's with an Arduino ISP. I am thinking a delay off of about 45 sec, with the probes about 1/4 above the intake should give the pump enough time to drop the level well below the probes. Thanks for any help. BTW...the detector circuit works flawlessly but I would never have figured it out without your vid...which was outstanding.

RanzelM (author)2014-11-13

Is this working?

rpérez23 (author)2014-01-07

I loved this, I built it and works nice with any NPN transistor! There is other question, how do I make it work the other way? to turn on the led when there is no water and turn off when water get the sensor? My friend briefle told me is siwtching the Variable resistor with the sensor, but I tried and It did not work, I am not sure if that would be. How cold you do it? like a Dry detector?


nervrunna (author)2013-07-31

Nice! below is a reverse engineered water sensor circuit. Its ancient, but it still works like a dream. Its an AC circuit, so it wont eat the electrodes and it
It takes two sensor inputs: One for sensing low tank level and the other for sensing a full tank level. It basically boils down to the ability to have for example an automatic fill system. So when the level gets to the bottom sensor, the pump comes on and fills it until it gets to the top sensor.
I drew the schematic directly from the board. It has old components and some of them Im not sure what their values are. If anyone could elucidate, it would be nice :


paxipatel (author)2012-06-16

how it works

mr_man (author)2012-06-13

I like that you put the 22k resistor in "Step 6", and this can be used in the circuit in "step 2" as well. It reduces the probe current, and protects the transistor in the event that the probe electrodes touch each other and short, and reduces the chance of electrolysis generating gas bubbles on the probe electrodes. Also to reduce electrolysis, you could just use 1.5 volts across the probes

Also with a 12 volt supply, you'll want use a higher value resistor than 330 ohms on the LED.

The circuit will probably work without the potentiometer.

sala89 (author)2012-04-04

how much cost of this project in india

manjotmessi (author)2011-11-05

please give me a detailed process of fuctioning of a transisitor in a water level indicator project.

mboruah (author)2011-10-07

is any other option not available,i m really not getting it.........

sahilaggarwal (author)2011-01-21

here transistor is used for amplification ??????
and why only BC547 OR 548 is used???

I know I have bad hand writing but it also says any NPN transistor will work

jpsailr (author)2009-09-26

After many attempts to make a circuit like this, I gave up. Reason: when current flows through water from one plate to another, gas builds up on the sensor plates and the conductivity of the water reduces until it is undetectable, over 10 megohms within minutes. So if you're not there right when it happens, you will miss it. I solved this by creating a circuit which would put an AC current on the sensor plates. This continually purges the plates of gas and keeps the resistance through the water to less than 100 Kohms - very useable. This test ran for over 4 hours with no loss of conductivity. Now I successfully use it to detect bilge water as soon as it happens, or water on the basement floor. I will submit a project when I get it written up.

MarleneL (author)jpsailr2011-02-24

I am working on a hybrid hot water system and need something like what you are describing... can you please forward me some more information on it please!! Thank you.

eng_tako (author)2010-10-19

thank you very much you help me alot

wonderingoutloud (author)2010-09-09

Assuming clean water, zero turbulence, very small inflow related to volume, could I get 1/32 inch level gage accuracy? In other words, under perfect conditions, what accuracy could one expect?

it is a circuit designed to give you a visual alert that you need to fill you water tank in a vehicle accuracy is not part of its implementation being cheep and simple is. If you wish to have a sensor circuit that is that accurate this is not the way to go. Why do you need such accuracy what are you trying to build ???

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