Introduction: Water Powered Flashlight

Picture of Water Powered Flashlight
Batteries are too mainstream, let's make Water Powered ones! The DIY flashlight never runs out of batteries, water is all around us and will never run out. One of today's causes of pollution is the improper disposal of batteries containing heavy metals such as lead and mercury. The answer, using water as electrolyte!

Imagine, running wall clocks for 6-12 months with water, you'll never need to leave your house just to buy batteries and there's no need to recharge them. What could be more convenient than replenishing your batteries with tap water? :D

The flashlight runs 30mins continuously with tap water and 2 hours with saltwater. Not bad for a single celled prototype :D This thing also works well with calculators, clocks & radios Remember, adding a second cell triples the glow and lighting time! 

How Does It Work?
This is a type of battery called the "Galvanic Cell", having 2 different types of metals and is connected by a salt bridge. It works like your typical battery but uses water as its electrolyte. If you want to read more about how batteries work "click here" The output voltage is pretty faint and isn't enough to run a single LED. By the help our trusty "Joule Thief Circuit", the LEDs would glow even at low voltages.

Is It Really Powered By Water?
Well not really, the water serves as an electrolyte, a replacement for toxic chemicals used in regular batteries, which usually ends up in dumpsites. So why call it water powered? Of course no one would be interested in the title "Galvanic Flashlight" plus that's what easily pops up in people's minds. The Redox reaction takes place in this project.

Practical Uses:
1st.) If you got lost and stranded out in the woods, you can't rely on batteries, eventually they run out. A mini version would save stranded people in the woods. Just go to the nearest river and fill her up! Whala, you have light!
2nd.) School science experiment
3rd.) A fun and educational project for all ages!

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A Larger Scale Water Powered Project (a.k.a Galvanic Cell):

Step 1: Gathering Tools & Materials

Picture of Gathering Tools & Materials

Parts & Materials:   
- PVC Pipe 4" Long (3/4"‎Ø)  [Local Hardware]
- PVC Coupling 3/4" to 1" [Local Hardware]
- Recycled 3xLED Torch  [Inventory = Free]
- Toroidal Core/ Bead  [Recycled From CFL Bulb]
- 2N3904 Gen. Purpose NPN Transistor [Radioshack] 
- 1K Ohm Resistor (1/4w) [Radioshack]
- Cooper & Zinc Strip  [Local Hobby Shop]
- Magnet Wire/ Copper Wire [Inventory/ Local Hardware]
- 4 Sheets Of Tissue Paper [Toilet/ Bathroom]
- 2x2" Sheet of Acetate [Bookstore/ Office Supplies]

Tools & Equipment:
- Leatherman MultiTool
- Soldering Iron
- Hot GlueGun
- Teflon Tape
- Super Glue

Step 2: Preparing the Power Cells

Picture of Preparing the Power Cells

The power cell is your flashlight's main source of energy. Basically there are two strips of metal, one for the anode and one for the cathode. The "Copper Strip" will provide the positive energy while the "Zinc Strip" for the negative. 

Procedures: Assembling The Power Cell:
1st.) Roll tissue paper around your "Copper Strip" until you reach the 3rd sheet.
2nd.) After reaching the third sheet, roll the "Zinc Strip" until you reach your final sheet, which is the 5th sheet.
3rd.) Now tie some copper wire around the PowerCell, this prevents your tissue from tearing once it gets wet.
4th.) I recycled a pulley since it fits snugly on the PVC Coupling, puncture 2 slits for the metal strips to fit in.
5th.) Insert both metal strips through the pully's hole and seal/ waterproof it using epoxy/ superglue/ hotglue.

Step 3: Assembling the Joule Thief

Picture of Assembling the Joule Thief

What's A Joule Thief? 
A "joule thief" is a circuit that helps drive an LED light even though your power supply is running low. What can we do with it? We can use it to squeeze the life out of our drained batteries. Bottom-line, this circuit makes LEDs glow even at low voltages.

Let's get started! Hummm, you probably encountered a joule thief before. Lucky for you I have a more detailed guide about making a simple joule thief found here: Making A Simple Joule Thief (made easy)

If you already know how to build one, you can just follow the simple diagram from above. I needed to make my circuit more compact so I soldered my transistor below the LED's board while the toroidal core was glued above the LED's board.

Click Me! Visit my full tutorial on building a joule thief.

Step 4: Combining the PowerCell & Joule Thief

Picture of Combining the PowerCell & Joule Thief

You probably came to a realization that the flashlight, uses to two separate projects, the PowerCell and the Joule Thief circuit, in order to work. 

For this step, solder the wires of the "PowerCell" to the "Joule Thief" then apply superglue around the coupling. Finally superglue the LED's reflector to your coupling.

Step 5: Preparing the Water Storage Cylinder

Picture of Preparing the Water Storage Cylinder

Get a 4" long PVC pipe then glue a small piece of acetate, this let's you see if the flashlight still has water. 

Step 6: Fill Her Up!

Picture of Fill Her Up!

Just fill in tap water and you are ready to go!

Attention: Tap water won't last for more than 30 mins. They lack electrolytes. Saltwater will boost to the flashlight's glowing time but still it would only last for 2 hours. Vinegar & Gatorade works best, since they both contain electrolytes (lots of them). 

Adding a second cell triples the glow and lighting time!

Tested Liquids As Fuel:
- Tap Water = 0.5v - 0.6v (@400 mAh)
- Saltwater  = 0.6v - 1v    (@600 mAh)
- Vinegar     = 0.8v - 1.2v (@850 mAh)
- Gatorade   = 0.9v - 1.1v (@700 mAh)

Step 7: You're Done!

Picture of You're Done!
Let's light up the world, with free energy! Also, don't be shy to share your own version of the Water Powered Battery, just leave a comment & photo below.

Thanks for Viewing!


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knexpert1700 (author)2013-11-07

Would a 9011 transistor work instead of a 2N3904?

ASCAS (author)knexpert17002013-11-07

Yes it would! :D any general purpose NPNs would work just fine!

manicmonday (author)ASCAS2015-12-24

There are many other very good Instructables detailing how to build a "Joule Thief" and how they work. You could have simplified this one by first referring people to one of those for that portion of the project.

nwlaurie (author)manicmonday2015-12-25

He did!

manicmonday (author)nwlaurie2015-12-25

No, he didn't. This instructable tells how to make a joule thief and does not refer readers somewhere else for that info.

nwlaurie (author)manicmonday2015-12-26

Under the heading 'How does it work?' he's put a link (labelled "Joule Thief circuit" to

xhp26 (author)2013-11-04

Impressionante !

xaviergoby (author)2013-11-04

Fantastic :D Love it! Great thinking!

icekid (author)2013-11-03

Oh dude thanks for this, voted too! We have an investigatory project for chem class. A project like this would do great. How about: "Testing the feasibility of galvanic batteries" (a.k.a "Water Powered") for the title?

ASCAS (author)icekid2013-11-03

That's a good title :)) Similar to our last year's IP title, about the feasibility of hydroponic planting.

rimar2000 (author)2013-10-30

Brilliant as always, Casimiro!

ASCAS (author)rimar20002013-10-30

Thanks sir rimar!

PsalmsS1 (author)2017-12-31

Can I use aluminum copper battery instead of zinc?

Annie& (author)2017-12-11

The first law of physics is: you can't get something for nothing. If this was as good as it seems, power companies would insert metals in the ocean and get free electricity forever. The battery has to wear out after so many "charges". They don't say how many. But here's a thought would make a great buoy or yacht light.(for as long as it lasted).

Battlespeed (author)2014-07-16

Very neat.

As an aside, this bugs me whenever I see it: "Whala" or "walla" etc. The word is "voila" - a common French word - and I also don't know why so many people think the word starts with "w" because the "v" IS pronounced - as in VWALLAH.

DaveL150 (author)Battlespeed2017-12-10

Hurrah, someone else noticed.

TimothyJ999 (author)Battlespeed2015-12-24

Thank you! That was driving me crazy.

SirCooksalot (author)TimothyJ9992015-12-28

This is one of my favorites too.... It's usually 'viola' which doesn't make phonetic sense either. Happy to see other voila police out there cleaning up the world.

DeepakB34 (author)2017-03-03

wow thats good

opeyemi.seun2 (author)2017-01-17

Nice Instructable bro, just wanna ask whether the readings are from open circuit or you have the LED module connected?

sconda (author)2016-12-05

This is really great community

I have found something that might also be of help to my colleagues here

You can follow this link for it

krille15 (author)2016-11-13

Can you build like a grid of this things and put them in a stream to get alot of power?

KDMartin (author)2016-09-04

Hey author! Will it work if I use detergent as an electrolyte
instead of water? I just want to know because my teacher wants us to
think of other liquid that could be use as an alternative for water.
Thanks a lot, hope you reply ASAP! :)

MistE1 (author)2016-05-22

Will urine be able to power the flashlight too? For example, if water is not available in a forest or something

Medelis made it! (author)2016-04-05

I'll Show You - How drinking water can deliver electric power ... Free Geen Energy without poison or toxins

This battery generates electric power out of Tap Water (drinking water or any similar liquid).... its small and powerful

battery will work about 3 hours (you can always refill water - make it work again)

GabriellaM3 (author)2016-03-12

Where did you get your copper and zinc strip in the Philippines? Is there an online store?

ReymarkB (author)2016-02-28


I have put two galvanic cells in series and I have a total output of 1.7V however when I connect the galvanic cells to the Joule Thief the output goes down to 0.5V hence the LED cannot light up. What am I doing wrong? pls help!

DragonWOF (author)2016-02-21

Do you have to use a joule thief?

DragonWOF (author)2016-02-19

Do you have to include the joule third to make it work?

ttyler333 (author)2016-01-20

Would be interesting to incorporate a battery trickle charger, a 50ma battery to "charge" even when the flashlight is off.

vmigas (author)2016-01-13

What if to make boat running on overboard water?)))

M4n0v3y (author)2015-12-28

Great project! More cells, combination of joule thief and cells, electrolytic fluid ( copper sulfide, water, etc..). There are too much to research! Nice strike!

Landroo (author)2015-12-24

This is a fun science experiment. I probably wouldn't go to all the trouble and mess involved, because there are plenty of better non-battery alternatives, including solar-cell, dynamo, or rechargeable flashlights available.

Bakzeil (author)Landroo2015-12-24

A flashlight is for use in the dark, so you wouldn't go anywhere with a flashlight on solar-energy, or you need batteries again. For a flashlight this is a very good alternative, I think.

Landroo (author)Bakzeil2015-12-27

I've never seen a solar-powered flashlight that didn't use a battery. Dynamo flashlights however, are always ready, and don't need anything but muscle power.

Railes (author)Landroo2015-12-24

for back packing, there is none better, as a avid survivalist, this one is pretty top notch.

dreiduke (author)2015-12-24

please excuse me, but this flash light is not water powered, but chemical powered.
And it does runs out of (Battery) it will stop working, when the more inferior metal is gone or oxided.
Its just a galvanic Cell.
Like these Lemon or Potato "Powered" Things.
These all are not powered by their electrolytes (Water, Potato, Lime or other,) but by their metals, "electrochemical series"

But its nice for emergency things, to keep them until u need it.
Its the same principle like those little Lights on Aircraft Life Vests.
there is a small Box with two holes, and at the inside two different metals separated by a kind of sponge.

ssj152 (author)dreiduke2015-12-24

He did say that it was a galvanic cell; please read the text again. Look for: "Is It Really Powered By Water?",

dreiduke (author)ssj1522015-12-26

yea i over read it, sorry for that.
never then less its a nice Project, as everlasting battery Flashlight if not used for in case of full blackout.
i was triggered by the headline, sorry also for that.

nwlaurie (author)dreiduke2015-12-25

All of that is exactly what the author said in the introduction!

MegaRCGuy (author)2015-12-25

Very good project !!!

SaunderyaT (author)2015-11-15

I cant seem to get it working ......everything is fine till the joule thief ........ but the power cell is where i get a problem ........i dipped it into water and salt water but my LED did not glow !!! please help !!!! i need to submit this as a science project tommorow !!!!

jmcdonald23 (author)SaunderyaT2015-12-25

LEDs only work one way. Try reversing the voltage

Yonatan24 (author)2015-12-24

Don't ou have to replace the electrodes every once in a while, I heard that they just wear out

ssj152 (author)Yonatan242015-12-24

Yes, this is an electrochemical reaction and will eventually exhaust the available electrons in the copper. See the other replies for suggestions for ways to make it last longer and be brighter.

Yonatan24 (author)Yonatan242015-12-24


Jkivance (author)2015-12-24

That is cool!

KROKKENOSTER (author)2015-12-24

Good ideas never die they kept on re-inventing themselves

KROKKENOSTER (author)2015-12-24

Good ideas never die they kept on re-inventing themselves

goldenskyhook (author)2015-12-24


If we're talking electrolytes here, I'm guessing urine might be right up there as a possible substance. Now THAT is survivalism.

About This Instructable




Bio: Hi I'm Angelo! I am a 18 y/o college sophomore taking my majors in BS-ECE at the DLSU. I use my course as ... More »
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