Water purification uses home-built electrolysis rig

If you plan ahead a little bit you could have your own system of water purification to use in emergencies. Everyone needs clean drinking water and this gadget will let your produce your own purification drops quite easily.

The solution contains chlorine, which is created through electrolysis. The PVC cap seen near the bottom of the image has two electrodes sticking out of it. These are titanium plated mesh plates separated by a rubber ring. The cap has a small hole in it to keep the flow rate low and the fitting at the top acts as a funnel. When you pour in a salt water mixture it passes through the energized plates and a chemical reaction splits the sodium from the chlorine.

A twelve volt power source is necessary for this to work. But since the electrolytic process takes just a minute or two you could easily source the power from batteries charged with solar cells. Check out a full build walk through and demonstration video after the break.

[Thanks David]


48 thoughts on “Water purification uses home-built electrolysis rig

  1. Uhh.

    When you pour in a salt water mixture it passes through the energized plates and a chemical reaction splits the sodium from the chlorine.

    It also produces chlorine gas. Which is fairly toxic. Might want to think this one through a bit more.

    1. Technically speaking, there’s two reactions going on. One electrode separates sodium, which turns into NaOH + H and the other electrode releases Cl which then react H + Cl => HCl and HCl + NaOH => NaCl + H2O.

      The whole thing goes around and comes back as long as the hydrogen and chlorine remain dissolved in the water. If either escapes, you’re left with a slightly alkaline solution because not all of the NaOH will react and the gaseous Cl and H will leave the solution.

      1. The end result is, thought, that the device doesn’t do what it’s supposed to do. The dissolved hydrogen will eliminate the dissolved chlorine very quickly, so if you let the solution sit for a bit, it just turns back to salt water.

        And putting ten drops of salt water into a gallon of dirty water just makes it slightly more salty.

      2. Your chemical reactions are right, but you’ve failed to consider gas solubility, and where each chemical is produced in an electrolytic system.

        Cl will readily dissolve in water. It’s produced at the anode, along with O2 bubbles which will carry some of it away (thus the need for ventilation); but the rest successfully dissolves.

        H on the other hand has almost zero solubility in water. It stays near the cathode, where it’s produced, in the form of bubbles. Only dissolved Cl that makes it over to the cathode area and directly contacts a bubble will react with it; which limits the reaction rate, and allows dissolved Cl to build up.

        So this really will produce a sterilizing solution, although there’s a practical limit as to how strong; because at some point, offgassing and reaction rates will exceed the rate of Cl production.

      3. What actually happens is:
        2Cl- => Cl2 + 2e-
        And 2H2O + 2e- => H2 + 2OH-
        The hydrogen bubbles off and chlorine reacts with hydroxide to form hypochlorite. Some chlorine will be lost, but it is sufficiently reactive that it will be a small amount.

        “if you are not part of the solution, you are part of the precipitate – you fall to the bottom”

      4. The reaction is as follows:

        Cl2 + 2 NaOH ==> NaCl + NaOCl + H2O

        I have potentially over simplified some of the chemistry involved (further oxidation to chlorate and decomposition of chlorine to hypochlorous acid for example), but for the short duration that the equipment is intended to be used for, it should be perfectly accurate.

    2. I’m quite amazed how everyone questions the chemistry behind this and not the practical side. If all you are making is bleach, wouldn’t a dollars worth of bleach be a whole lot simpler?

      The title of this should be “Rube Goldberge Water Purifier”

    1. Actually it is never created (see my comments above). Water is much easier to oxidize than sodium ion, hence you get hydrogen gas and hydroxide. The electrolysis of molten salt will give liquid sodium though – it is a well known industrial process.

      1. And the chlorine is created on one electrode, and the hydrogen on the other – the hydrogen would leave the solution quickly, while the chlorine dissoves in water and reacts with hydroxide. Reaction of chlorine with hydrogen gas under these conditions is unlikely to compete.

    1. How about read a book to understand what you are doing before you do it, so you can accomplish it with a degree of safely? Hacks are, by definition, hacks but they don’t need to constantly repeat the same mistakes over and over again (editors who constantly post PVC base air guns, I am looking at you).

  2. The US Military has a water “purification” device based on this principle, but it seems that there is confusion by the article’s writer as to how this device operates.

    It does not produce chlorine to sterilize the water, as the chlorine produced in an undivided electrolytic cell such as is pictured would be quickly eliminated.

    The idea is rather, sodium hypochlorite [and to a much lesser degree sodium chlorate] are produced when chlorine reacts with NaOH which is produced by the oxidation of sodium ions at the other electrode.

    Sodium hypochlorite, better known as household bleach, is a very effective disinfectant for water at the few drops per gallon level.

    Sodium hypochlorite has been produced by the reaction of Cl + NaOH since it’s discovery, and this is how it is indeed produced at the industrial level even today.

    Here’s a couple of handy links which describe the situation a little better:



  3. Just to clear it up this will produce chlorine (gaseous), hydrogen (gaseous), and aqueous hydroxide. The chlorine can react with the water to form hypochlorite (bleach) and muriatic acid (which as mentioned results in a net reaction of nada) or degas from solution as will the hydrogen. So its good for cleaning atleast.

    1. No hcl is ever formed in this hydrolysis ( i am on a quest to teach you guys basic chemistry:) see my comments above. Chlorine in a water solution will decompose to hypochlorous acid and hcl in the prescence of sunlight, but that is unlikely since most of it will have already reacted with hydroxide to form hypochlorite. The overall stoichiometry of all of these reactions is quite complex.

  4. Doesnt work. dont use this. Use all the PVC to make a sand bed water filter. if you still need to kill what get’s through all that, boil the water. you can use a solar still to do that task.

    Honestly people, water filtration is NOT hard, stop trying to use OOgy-Boogy science to achieve shortcuts.

    And this is not science, it’s screwing around. Sciece is based on real knowlege and existing systems that are known to work.

    and yes I know a lot more about the subject that all of you. I still hold a F-1 Water Treatment License, and have 6 years of college for Water chemistry, and water microbiology.

    I know how to kill and filter all the nasties out of water, and it’s NOT done the way you see in this “hack”.

    1. I wholeheartedly agree that filtering and boiling would be a more effective process. BUT you can make some damn handy chemicals with electrolysis including sodium hydroxide(lye) and sodium hypochlorite(bleach).

    2. Seems like you’ve got a touch of profession-itis there. Ready to poo-poo any method that isn’t how it’s done in industry, shout “oogy boogie science”, and wave supposed credentials at you; while simultaneously not demonstrating any of the expert knowledge they claim, like an actual scientific reason why this won’t work. Come to think of it, I’ve met another water treatment expert, and they acted the same. Must be something in the water. ;)

      This isn’t for normal or large-scale water treatment. It’s for survivalism, which is all about preparing for theoretical worst-case scenarios. Like organic contaminants that neither filtration or boiling will remove. Or needing a drink now, when your water supplies have run out; and your solar still won’t work because it’s overcast.

      Even the author of the hack made it clear that this is a relatively expensive and inefficient fallback option, which may be of value only if all other options fail. It doesn’t take a water treatment expert or survivalist to understand that.

      1. Why how dare you question fartfaces experience, if you came around here enough, you would know that he knows absolutely everything! if he didn’t think of it or approve of it, it’s absolute garbage. The site could just be renamed ‘fartface shits on your idea-a-day’

        I think someone actually made a greasemonkey script a while back just to escape his shadow of greatness, for it is quite depressing to know you’ll never compare. (Fear not, he’ll remind you if you aren’t sure about it too.)

  5. Funny but I was expecting an electrolysis system that would then feed the hydrogen and Oxygen into a fuel cell to recover a part of the energy used to split the water. You should get pure water out of whatever you put in.

    1. What happens when that gallon of bleach is used up? Or spilled?
      Or neighbors come by and need some too?
      The guy in the video says he bought a “lifetime supply” of HTH, and that this device was a backup plan.

  6. Wow I knew the HaD crowd was harsh but really saying this doesn’t work is BS.

    mr fartface what happens when your water treatment plant fails and you have 10,000+ people needing water, OOO that’s right you use Clorox acquired at the local store and added at the right concentration for that systems supply need. until you can fix the plant, OR you issue a boil notice and people get a bit upset and lose trust. since you can have a “few” bad days on your water tests a few days of running Clorox saves your job.

    AND HOW do they make that fancy Clorox.. I wonder. could it BE? NO say it isn’t so..

    Our friend electrolysis!


    Steve0 – the mesh is only for protection of the electrodes, optional and the vid used a plumbing part rather then mesh. If your referring to the electrodes I am sure you can use others however you need to be aware of what they will break down into and become part of you “solution” :)

    I have been an avid hiker for years, using all sorts of water sanitizing methods, filters, iodine tabs, and MIOX. This process works. I own and have used and DRANK the water from the MSR MIOX water “treatment” system. Its EXACTLY the same process.

    Water+salt+electricity= sanitizing solution.


    Developed for the military it uses 2x 123A batteries, fill the cap with salt, put in about a tsp of water, mix and press the button, it has a timed pulse that will increase the strength of the solution each time till that one spoon full of water turned MIOX is good for treating about 4L of water. takes about 5-20 seconds to create the solution, then add. wait 30m to 4h. After about 4 hours of dwell time it will even kill/inactivate cryptosporidium. EXACTLY what this video is demonstrating.

    You can just use Clorox(unscented plain) at about 1-5 drops per gallon. One thing to note is that this video/build doesn’t even consider that varying water supplies will need varying amounts of treatment. The MSR system includes a “free/available chlorine” test that you can use after treatment to check to insure adequate treatment.

    PUR makes a different sort of product


    Targeted with a different demographic in mind but if your looking for shelf stable long term system that doesn’t involve electricity or machines in general and the bottle of bleach was used on the laundry before the disaster hit. then consider having a supply of these things till you can build a MIOX making CPU. Their product uses flocculation to clump contaminates into an easy to filter sludge while at the same time disinfecting the water. The system consisits of ferric sulfate the flocculant and calcium hypochlorite as a stand-in for sodium hypochlorite aka bleach/clorox.


    You can use alum in place of ferric sulfate.


    Chances are your local municipality is using this EXACT same technology to treat your tap water. Making the sanitizing solution on site is safer and cheaper then shipping hazardous materials or using expensive filters. Filters like reverse osmosis is only reserved for the hardest to treat water. One additional hazard to worry about is that chlorine treated water will contain things that may be of concern.


    One could make activated carbon and improvise a carbon post filter for the treated water if one was extremely concerned about the post treated water.


    And should you need it you can make Activated carbon just don’t get confused and just make charcoal without actually using some process to activate it. In the DIY theme you can use calcium chloride to make activated carbon. Or use calcium carbonate and sodium chloride to make calcium chloride to then use to make activated carbon.

    Long story short nice video. For the zombie apocalypse you may want to stock up on some common useful precursors, if you have a chance go for the “reagent/acs/usp” grades or you may end up with some nasty surprises from the lower grade chemicals..

  7. This system is used in large scale contrary to some of the other comments.

    I work on an oil rig where we have an electrochlorinator unit which produces large volumes of hypochlorite to treat seawater beforw its used as cooling water (kills everything so the coolers dont clog up with seaweed and muscles and stuff). We also use it in the drinking water (produced from seawater via an RO unit).

    Its made up of cells containing stainless plates running at about 440v with current control.

  8. to be honest i don’t know if this will work at all or how the military counterpart is supposed to work. but one thing is sure assuming it works this isn’t meant as a single step water purification apparatus.
    why am i so sure?
    a) killing the microbes is only half the job. many bacteria and fungi contain endotoxins in their cellwalls which will make you sick no matter if the organisme is dead or alive
    b)no filtering of particulate matter
    c)no chemical “decontamination”

    if you think of this setup as an emergency water purifier then you should assume that there is no mains power. batteries or generator run out eventually not to mention the cost. if you assume that for some reason there is mains power then there are definitively better options to make clean water. distillation being the easiest and cheapest one.
    to make this setup efficient as it is i would definitely add a filtering and activated charcoal stage.

    1. Some good points here. But I would definitely consider a bicycle an essential part of any survival plan. And if you attach a generator to it, you have enough renewable electrical power to run this purifier.

      Like you, I think knowing how to handle such scenarios “just in case” is a good thing; even if I’m not rushing out to stockpile stuff.

  9. No offense, but this is pretty typical of hackaday. 1) Find a “hack” online 2) Re-post “hack”, having no idea how it works and completely ignoring blatant errors 3) Defend to the death

    Lol… If you put contaminated water in this gadget and try to “purify” it, then drink it… You are going to get sick.

    Hackaday, stop re-linking re-linked crap. Maybe do a little vetting before you even think about linking to something. This post just exposes how clueless you guys are.

  10. Koplin beat me to the punch! As I was reading this, I was thinking about Miox! This is essentially the same process!

    As someone who lives without municipal water, I went a little crazy researching water purification processes a few years back before I moved into where I live. Although it may seem scary and daunting at first, considering you’re talking about the health of you and your family, knowing what type of contaminants may be in the water is a major requirement. This requires periodic if not continuous monitoring of the incoming water supply. But in an emergency scenario, such that I was preparing for, there are but a few ways to remove most of the contaminants in water in one single step.
    Snow is right. Water “purification” is not a single step process as I hope fartface would agree with his many years of schooling. I have to say, I spoke with many water treatment specialists, including a few close family members. They all agree that the way a municipality system works isn’t the safest. Its a balance between cheapest and “safe enough” for the general public. Private water treatment usually uses a combination of ultra filtering (Reverse-osmosis), ultra-pasteurization, and distillation. These methods are cost-ineffective, not to mention time, fuel and labor intensive for a survivalistic standpoint, but may be adapted down to work on a small scale with a renewable energy source. Nothing is impossible with a little bit of ingenuity (and money)!

    Getting back to the actual hack, sure its a good proof-of-concept, it works and needs a few rough edges smoothed out, and he did not indicate that this should only be one of a multi-step process, but at least he’s documenting and sharing his findings! It is a proven process that has been used in industry for decades. I’m not saying its the best way to do it, but sure is an excellent piece of knowledge to file away and bring out for a “just-in-case” scenario!

  11. The builder used 12 gauge wire and 30 Amp battery clamps. I can understand the clamps being large if you were planning on hooking up to a car battery, but why 12 gauge wire? That size wire sort of implies a current of 15 to 20 Amps. Wow! Does anyone know what the actual current demands are for this device? My guess is that it should be something in the range of milliamps and thus wire size could be much smaller.

  12. With 12 volts why all the worry about arcing? Unless he meant shorting. Need is relative, and one can “what if” preparedness beyond practical. 2 gallons of bleach isn’t going to break the bank and will treat a lot of water to the extent that chlorine can make it saver. I’m my own water utility with my water well,and water that doesn’t require treatment. Not that this isn’t an interesting project, but not one I see myself needing.

  13. why complicate things w/ excess?aaaaaaaDig a small hole in ground or sandy beach.Piss in hole Put cup in botom of hole w/ a bit of tubing you can suck h20 out of cup/.Cover hole w/ plastic and put a small rock etc in middle of plastic above cup. when sun hits contraption h20 vapour hits plastic and ru ns dowm to cup. suck water out. simple. no batteries etc and your drinking clean distilled water.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s