How to Use Calcium Hypochlorite for Water Purification

How to use calcium hypochlorite for water purification. www.TheSurvivalMom.comWhen I was writing my book, Survival Mom, I was a real stickler for accuracy. Chapter 2 is all about water storage and purification, so I went to water expert Alan Martindale who is the Water Quality Supervisor for the City of Mesa in Arizona with all my unanswered questions about water safety.

I asked Alan about the use of calcium hypochlorite, aka pool shock, for purifying water because I wanted an expert to weigh in on this popular survival and prepper topic. I’ve written directions for its use in purifying water here.

Here is what Alan had to say:

“Lisa, I would agree that calcium hypochlorite can be used to disinfect water.  As you mention, the key is to make sure it is intended to be used for purification of drinking water.  The standard for this is National Sanitary Foundation (NSF) approved.  Calcium hypochlorite can be purchased in several concentrations. Although 65% is most common, you will also see 78% available chlorine.

Need to be real careful with chlorine concentrations.  You shouldn’t really drink much over 2ppm (parts per million) or it can cause diarrhea.  The maximum contaminant level (MCL) set by the EPA for chlorine is 4ppm.

Figuring chlorine concentration is based on weight.  Cal-shock 65 is 65% available chlorine so 1 pound = 0.65 pounds chlorine.  0.65 pounds (10.5oz) chlorine will treat 60,000 gallons of water to an initial residual to 1.3ppm!  To treat one gallon to 1.3ppm you would use 0.65/60000=  0.00017oz calcium hypochlorite.  1 ounce will treat about 5700 gallons.  These numbers are hard to understand and apply at small quantities, like a few gallons.

I read on one website that one granule, the size of a period, would treat one gallon and 1/8th level teaspoon would treat 55 gallons to 5ppm.  Sounds about right but I can’t confirm!

A huge issue associated with chlorinating is the “chlorine demand” of the water being treated.  If one water source has more contamination than another, it will take more chlorine to make it safe. Could be two or three times more.  Many emergency sites recommend having some test equipment to verify chlorine residuals. A pool test kit or test strips will work just fine.

Now having said all this, I probably complicated your issue.  Bottom line, calcium hypochlorite will work great but, it will take more experience and care to get safe results than using unscented laundry bleach.”

Pool test kits are inexpensive and can be purchased just about anywhere pool chemicals are sold. I recommend that everyone who owns calcium hypochlorite and is planning to use that as a way to purify water have at least one pool test kit on hand. That will be the best way we amateurs can determine that the chlorine level of our purified water is safe to drink.

As Alan states, using store-bought bleach is easier (8 drops per 1 gallon of water for purification purposes), but bleach has a shelf life. It begins to lose its effectiveness after several months, thus the popularity of calcium hypochlorite in survival circles.

Resources mentioned in this article:

There may be links in the post above that are “affiliate links.” This means if you click on the link and purchase the item, I will receive an affiliate commission, which does not affect the price you pay for the product. Regardless, I only recommend products or services I use personally and believe will add value to my readers. 

© Copyright 2012 The Survival Mom, All rights Reserved. Written For: The Survival Mom
The following two tabs change content below.
I'm the original Survival Mom, and have been helping moms worry less and enjoy their homes and families more for 5 years. Come join me on my journey to becoming more prepared to handle everyday emergencies and worst case scenarios.

I want to receive updates and
EMP survival reports!


  1. Jim Ramsey says

    Last week, I read an article that discusses some of the dangers of Calcium Hypochlorite. I don’t remember exactly where it was, but Prepperwebsite was the path to it. It was said that one must take care in the storage method, because it will eventually deteriorate the container, unless all glass. Also, when in a sealed container, the decomposition generates chlorine gas. If one does not take care when opening the container, breathing the fumes would become quite an immediate health problem. Perhaps some cautionary disclaimers are in order?

  2. Tim Reichert says

    I’m a sales rep for a large specialty chemical company that for years have sold Cal Hypo in both solid pucks and granular for pool sanitizing. Most states require 1 ppm as the lower threshold for pools and 5ppm on the high side. The problem is all forms of chloring degrade with time, so exactly how much to use in any “recipe” can change depending on how old the cal hypo is. What I want to find out is to what level (in ppm) do we need to achieve for proper bacterial kill? That is the question we should all need to know. If it’s X-ppm, then so be it. Even if the level is 50ppm, one can prep drums of contaminated water, killing off the bugs, then park it as the chlorine will gas off in a short time, faster in sunlight. But the question is how much to we mix to? 5ppm, 50ppm? If a pool operator has a swimmer that either vomits in the pool, or a child with diarrhea, the pool has to be evacuated and super chlorinated to at least 25 ppm for 24 continous hours. So is that the threshold for untreated water? I don’t know, but don’t want to risk getting very sick by under treating the questionable water. Perhaps Alan could shed more specific light on this…

  3. Tony says

    Can’t a person use the chlorine concentration to make a potent bleach solution and than better manage the amount of product to treat smaller water supplies. For example, make into solution and than just use drops to purify a gallon or two at a time?

    • Water Operator says

      I am a water operator in a chemical plant, the EPA and each state has the required minimum chlorine residuals on their web sites. In my state the bare minimum for free chlorine residual in distribution is .2 ppm. Residual free chlorine is what is leftover after the demand is met. So depending on the condition of the water you are treating, depends on your dosage. Checking for the remaining residual is the safest way to ensure your drinking water Residuals. FYI our maximum residual is 4.0 ppm free chlorine residual. I would, if i were forced to treat water at home, personally like my residual somewhere in between the two say, 1.0 – 1.5 ppm. Water treatment is more complicated than applying chlorine. Some nasty critters are chlorine resistant, and must be filtered. The water that comes from your tap, is monitored and treated with very strict restrictions, by licensed professionals, just saying.

      • says

        Thank you so much for sharing your expertise! My usual source for this information, Alan Martindale, has possibly retired from his position because I haven’t been able to get in touch with him. I appreciate your input.

        • Water Operator says

          You are so welcome. I just finished your book, I loved it, read it in a day and a half. I couldn’t put it down. It was refreshing to read it from a common sense perspective, since the topic is seemingly overwhelming. Looking forward to the next one!

  4. says

    I know chlorine is utilized for water treatment. Not only in swimming pools but even on water used for drinking and other personal purposes. We really need to know how water treatment works using certain chemicals, this one is a good source.

  5. says

    It’s a good thing you discussed important points about the use of calcium hypochlorite for water purification. Just the right kind of information everyone needed to know. I hope you come up with more of this kind of posts. We all know how chlorine works and where it’s utilized. It’s important that we know the pros and cons about it.

  6. Tony says

    It most certainly is hard to follow, especially when you need to vary your quantities of chlorine based on how badly contaminated the water is. It would seem a difficult task to figure out what is more contaminated than another.

    So, moving right along, how does iodine fare in the scheme of purification vs chlorine? Is it more reliable, or is it less reliable than chlorine?


    • says

      I’m not a big fan of using iodine because it comes with so many warnings for its use. The Red Cross uses a combination of boiling water AND using bleach, so in scenarios in which water is significantly contaminated, that is my suggestion as well.

  7. Carol says

    I just clicked the ‘here’ link to get 100% calcium hypochlorite. the only problem is, they have SEVERAL items listed on that particular page and I have NO idea WHICH one is the 100% pure stuff. Can you help?

  8. Cheryl says

    Hi, I was reading all the comments about the calcium hypochlorite and the problem with the proper amount to use. One thing that I have stored up on is brita filters for this very reason. From my understanding the brita filter does filter out the chlorine. I plan to use the calcium hypochlorite first and then filter through a brita filter just to be sure I get at least most of the chlorine out. I also have the Katadyn Ceradyn Water Microfilter but it does not filter chlorine, thus the brita.
    I did find an article a long time ago, this is what it said regarding the amount to use.
    Using granular calcium hypochlorite to disinfect water is a two step process.

    • To make a stock of chlorine solution (do not drink this!) dissolve 1 heaping teaspoon (about one-quarter of an ounce) of high-test (78%) granular calcium hypochlorite for each two gallons (eight liters) of water.
    • To disinfect water add one part of the chlorine solution to 100 parts water to be treated.
    • Let the mixture sit for at least one-half hour before drinking.

  9. phillip fielder says

    I would not rely on the Britta water filter ; I would use ZERO water filter(Much better) ; check results @ Healthranger , not sure of website , but just Google Health Ranger & you can find it ; You really need to see the TEST Results ! ZERO water Filter is the BEST you can buy in the “WORLD” as far as I can ascertain ; BEST water is “DISTILLED” , I have been using Distilled for over 40YRS. , I’am CLEAN !

Leave a Reply

Your email address will not be published. Required fields are marked *