Disinfection With Sodium Hypochlorite

In order to prevent disease all water should be disinfected before drinking. The most common way this is done in North America is with chlorine in one form or another. Chlorine comes in three main types, chlorine gas, sodium hypochlorite and calcium hypochlorite. In this article I will focus on sodium hypochlorite.

Sodium hypochlorite has another name, you probably know it better as bleach. The active ingredient in commercial bleach is sodium hypochlorite. This is commonly available in 6%, 12% and 15% solutions. Sodium hypochlorite has a relatively short shelf life. The shelf life is dependent on, sunlight, temperature, vibration, and the concentration. As each of those things increases the shelf life decreases. Ideally it should be stored in a cool room in an opaque container. Try not to shake the container during transport. As for the concentration, the higher the concentration, the faster it breaks down. But the stronger it is, the less room you need to store it. Also, if comparing a 12% solution to a 6% solution, the change will be more apparent in the stronger one, but as it breaks down the reaction slows down too. When the 12% reaches the 6% level, it breaks down like the one that started at 6% did on day one.

At work we use 12% sodium hypochlorite as our primary disinfectant. In the time it takes them to ship it too us it is already at 10%. When we do any calculations on dosages or concentrations we use 10% as our starting point. The good thing is the decline is predictable if you control the environmental factors. Now even at 1% the solution can still disinfect water, it will just take more of it. This is why I don’t like to give formulas like 30 drops, per gallon or whatever, honestly I don’t remember any of the recommended formulas. I don’t remember them for one simple reason, they all tell you to keep adding till you smell bleach after 30 minutes. The smelling is the key, if you can smell it 30 minutes later then you still have a residual of hypochlorite in the water and the demand for chlorine has stopped. Meaning if you can smell it, disinfection has been achieved assuming some time has passed. If you can’t smell it then there may be some demand for chlorine left in the water. The reason they all say smell, is because it is assumed everyone can smell bleach. The truth is, if you can smell it, then yes it is disinfected, but also disinfection was achieved well before you can smell it.

Purchasing a chlorine monitoring kit will help you better manage how you disinfect your water. The one I use is about $300 and it works perfectly. You can also get adequate information from the cheaper pool monitoring kits. Spend what you feel is appropriate. I’m not selling anything. But I recommend having a test kit over using your nose. I work frequently with the 12% strength hypochlorite solutions and I frequently come home to “You were using bleach again weren’t you?” my wife can smell it but I can’t smell a thing. My nose has become desensitized to chlorine and her nose can pick it up from twenty feet away. I would not want to depend on my nose or anyone’s nose in an emergency/SHTF scenario or even on an ongoing basis. The human nose just isn’t accurate enough. Maybe I am just picky, or have some professional snobbery/aversion to the, “smells disinfected” method. Or maybe I just want to be sure that the water I am drinking is safe for me, and my family to drink.

Sodium hypochlorite is an oxidizing agent, and a pretty strong one at that. This is what makes it such a good disinfectant. Many other disinfectants are also strong oxidizers. The chlorine literally removes electrons from the outer shell of living organisms, destabilizing the structure until that organism is dead. When sodium hypochlorite (NaOCl) is added to water it forms the OCl- ion, this is the hypochorite ion or what is called free chlorine. This is not to be confused with chlorine gas Cl2. Free chlorine is what most municipal water treatment facilities use for disinfection.

When hypochlorite is first added to water, it will disapear as things present in the water will reduce the chlorine to nothing. The second stage the chlorine bonds with ammonia compounds present in the water to form chloramines. It will also react with any organic matter in the water to form chlororganics. Some chlororganics are carcenogenic and I stress the need for removing as much organic material before you add chlorine of any kind. Non organic compounds in the water will just use up chlorine and protect some bacteria from the chlorine. Settle and filter your water before disinfecting. As chlorine is continually added, the chloramines and chlororagincs are partially destroyed, some will always remain. When the levels of chlorine start to rise, then disinfection has occurred. Any chlorine added beyond this point will remain as a disinfection residual. A good disinfection residual is essential for storage of water for any length of time. Below is an illustration of the breakpoint chlorination curve which is the official name for the process I described above.

Breakpoint Chlorination Curve: This is what happens when chlorine is added to water.

If you are storing large amounts of water for a long time it may be useful to change away from the free chlorine residual. In the curve above, free available residual may be converted to what is called monochloramine. This is done by adding an ammonia (NH4) solution to the chlorinated water at a ratio of 4:1 (free chlorine to ammonia). Monochloramine has a much longer shelf life and has no known negative health effects. It is a much weaker disinfectant and usually isn’t used for primary disinfection. It is however perfect for secondary disinfection. If you remember my article on disinfection (or go back and read it) secondary disinfection is the prevention of re-contamination of potable water. I will mention again, always use the highest grade chemicals for adding to drinking water. ANSI/NSF 60 is the standard for drinking water chemicals. Ask for this grade whenever purchasing chemicals. It will cost more, and you may have to order it from a supplier, but it will be free from other chemicals, most notably, household bleach contains arsenic, a poison, which is absent from the NSF 60 grade. In a total breakdown of the water system and you are only drinking this way for a short time, then the arsenic will be harmful on a much longer timeline then the pathogens in the water. The pathogens can kill people in a matter of days, arsenic will take years. I will leave you with the final message, always disinfect your water before drinking it. The method doesn’t matter, each have their own advantages and disadvantages. Choose the method that best suits you.


9 thoughts on “Disinfection With Sodium Hypochlorite

  1. OK, I’m focussing on emergency preparedness and needing to be self reliant for a short time period (at the extreme, let’s say 2 weeks). I have enough bottled drinking water for 3 days, and gas to run my generator, which runs my pump and can get water from my well for an additional 4 days. The back-up plan is a nearby lake – filled with germy ducks, recreational boats, dogs and swimmers – not water I will be drinking without treating first. How much bleach should I keep on hand? (this is the cheap stuff that I’m going to buy at the grocery store). And how long will it last on the shelf (in the cool dark basement) before I should replace it?

    • 1) always unscented bleach 2) without seeing the water I will say one 1gal container should suffice 3) consider replacing after a month to two months. A rotating supply that you use for laundry and cleaning will ensure you always have enough fresh bleach when you need it

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