DIY 12 Volt Chlorine Producing Unit for Water Purification

Today’s project is a device used to create a practically inexhaustible supply of the same disinfecting solution as the calcium hypochlorite makes. IF you want to go off grid, you have to have a supply of safe drinking water.  This instuctable shows how I built an inexpensive way of purifying water.

I have found that American missionaries that work in the third world are an excellent supply of information in what some call “appropriate technology” This is people centered, small scale, labor intensive, energy efficient, environmentally sound devices and processed. It’s a lot like “Macgyverisms” from my favorite 80’s TV show. He had advanced knowledge and primitive supplies and was able to cobble together 1900’s level tech with modern scientific principles.

One famous example of this is the CD3WD which is a collection of appropriate tech, Travis Hughley and barrelponics (which I AM going to build one day) and Safe Water International Ministries the developers of the CPU that is the focus of today’s article.

SWIM has developed the CPU to provide a chlorinating solution for water disinfection in third world countries. I would highly recommend you check out their website and consider donating to their mission as they are doing wonderful work.

If you want a CPU, but don’t have a DIY gene or interest in building one yourself, SWIM sells complete CPU tool box kit which includes an instruction card, a chlorine test kit, 2 mixing bottles, a salt measuring cup, and a couple of solution droppers. All you need to provide is 12 volts of electricity, salt, and water. A donation of $150 to their ministry would support this kit.

I wanted to turn this into a project so I gave a $50 donation and received the anode and cathode from them. They will email you the plans for free if you contact them on the website, and they have a technology link online with the instruction manual and a basic lesson plan for teaching this to others. I will warn you, the cathode and anodes are the main expense in the CPU, and you may have a hard time finding a supplier. One is a titanium mesh; the other is a mixed metal oxide (ruthenium).

However, I must tell you that their primary mission is to provide these units for missionary work in third world countries, so if demand causes a supply backlog, I would imagine they would fill that need first.

Basically what happens is when you bridge the electrodes with a salt water solution and apply an electrical charge to them you start a chemical reaction called electrolysis. In this particular process the water bubbles and produces a caustic chlorine solution roughly half as strong as laundry bleach. After the 9/11 attacks many municipal water treatment plants converted to this process so that they could remove their one ton chlorine gas tanks from their sites to mitigate their attractiveness as a terrorist target.

Per the SWIM for Him website the directions for use are:

1. Mix salt & water solution ( approx. ¼ cup salt to 16 oz water)
2. Connect wires to 12 volt source (negative, or black, to negative; positive, or red, to positive)
3. Pour the saltwater solution through the CPU into another bottle (observe the bubbling process)
4. Carefully repeat the pour-through process 5 times.
   1. This is different from a chlorate cell as that the water free flows through the unit which does not allow chlorates or perchlorates to form. This process operates at a different voltage and a much lower temperature.
5. Unhook the battery wires.
6. Rinse the CPU by pouring clean water through it.
7. Add 10 drops of the solution for each gallon of drinking water.
8. Wait one hour before drinking.

Additionally, if you are using solar power to charge your battery, you will want to recharge it for 3-5 hours after this process to ensure it is fully charged.

You will also need a test kit to ensure you use enough chlorine solution to properly sanitize your water supply.

This was a very simple project and I built the device in under an hour, I have to wait about 24 hours for the sealant to set, and then another 30 minutes in finishing touches. Please watch the video below to see all the steps.