Simple Water Sensor


Introduction: Simple Water Sensor

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

Step 1: 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

[Play Video]

Read Circuit Diagram

Step 3: 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

Build time will update once I make the PCB

Step 5: 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.


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



  • Casting Contest

    Casting Contest
  • Make it Move Contest

    Make it Move Contest
  • Clocks Contest

    Clocks Contest

We have a be nice policy.
Please be positive and constructive.




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.


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

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

5 replies

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

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.

an option would be to use gold electrodes


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! ...


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

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

1 reply

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

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?

5 replies

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)?

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.

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.

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

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.

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 ?

Can you show me the diagram in PCB ?

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