Calcium Hypochlorite for Treating Drinking Water, The Good and the Bad

Calcium Hypochlorite

For several years, I have seen many people recommending calcium hypochlorite for water purification.  They are providing correct information in that calcium hypochlorite will treat water if used correctly.  A pound of it will treat thousands of gallons of water and will cost you less than $10.

Before you rush out to buy some, I want to warn you about a few things that can get you into trouble or even killed.

Proper precautions must be taken while handling and storing calcium hypochlorite. Always follow the manufacturer’s instructions.  Calcium hypochlorite is a highly reactive material and can have a violent reaction if it comes in contact with incompatible materials.  I would recommend that you store it in the container in which you purchased it.  If you ask, the sales people should give you a MATERIAL SAFETY DATA SHEET or MSDS.  This will tell you about the hazards associated with this chemical.  You can also download one at

At a bare minimum, I would suggest you read Section 10 – Stability and Reactivity see below.

Section 10

“Stability…… Stable in optimum storage conditions. Heat, sunlight and contamination could cause decomposition.

Incompatibility….. Acids, reducing agents, combustible materials such as wood, cloth, or organic materials, dry powder fire extinguishers containing monoammonium phosphate (the ingredient in most fire extinguishers), metals such as iron and copper and their alloys, water or steam, ammonia, urea, amines.

Hazardous Products of Decomposition.  Water in contact with calcium hypochlorite releases chlorine gas.

Contact with incompatibles presents an explosion and fire hazard.

Toxic or corrosive fumes may be liberated. These include chlorine gas.”

As you can see just by reading section 10 above, the material can present some problems.  The entire MSDS is 8 pages long, I recommend you read it.

An additional problem is that there is some confusion on what type of pool shock to purchase.  Today I was in a big box store and saw products marked chlorine granules with the label stating they were for pool shock.  I checked the ingredients and they contained 99 percent Sodium Dichloro-S-Triazinetrione.

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Use only products that does not contain algaecides, fungicides, stabilizers or clarifiers. The label should list only Calcium hypochlorite and inert ingredients.  The Minnesota Department of Health publishes a list of all the brands of pool chemicals that are approved by the EPA for use in treating potable water.

How to Disinfect Water Using Calcium Hypochlorite

It is a simple two-step process

1. Make a chlorine solution by dissolving 1 heaping teaspoon (78%) granular calcium hypochlorite for every two gallons (eight liters) of water.  If your calcium hypochlorite is a weaker percentage, then increase the amount you use.  This mixture is not for drinking and is similar to chlorox.  Once this mixture has been made, it will start to degrade and will start to lose its strength in a matter of weeks, do not mix it in large batches.

2. To treat water, add one part of the above chlorine solution to 100 parts water to be treated.  This is approximately 1 pint (16 oz.) of the chlorine mixture to each 12.5 gallons of water to be treated.  Let the mixture sit for at least one-half hour before drinking. If the water has a strong chlorine taste let it sit for a few hours or aerate it by pouring from bucket to bucket.

Personally, this is not my favorite way to treat water, I don’t like adding chemicals to my water.  However, I do store calcium hypochlorite for backup.  I would also use the chlorine mixture as a disinfectant for things like bathroom personal cloths.


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10 thoughts on “Calcium Hypochlorite for Treating Drinking Water, The Good and the Bad”

  1. I’m in need of more guidance, please. I’ve experimented with the “heaping teaspoon” measurement using measuring spoons of different shapes. When weighed on an electronic kitchen scale, I get very different readings (grams). Is there a way to accurately measure the potency of the disinfecting solution created? Or should the treated drinking water have a minimum chlorine level to start the disinfecting process, and a not-to-exceed level when it will be safe to drink? A meter? A pool test kit?

    I’ve noticed many of my very senior neighbors are losing their sense of smell as they age, so relying on the sniff test might be dangerous as my sense of smell might also be declining.

  2. Iodine has its problems as does boiling. Chlorine has a few uses which make it a valuable asset to have during emergencies.

  3. I have a 550 gallon plastic potable water storage tank. If I did the math right, 3 heaping tsps. in 6 gal of water treats 600 gallons.
    Once I treat the freshly filled tank, how manyweeks, months or years before I need to treat it again to be sure it is drinkable. This is for future emergency use, not today for daily consumption.

    1. As long as that tank is tightly sealed, there’s no need to treat it again. The water might taste stale, so before drinking it, you could always run it through a purifier like a Berkey.

  4. All the instructions I can find online say to make this extremely dilute solution, then use that to treat more water. Nobody seems to give workable instructions for a 1000 gal tank.
    Can’t I just dilute ALL I need in a gallon or 2 of water, and dump it in?

    1. Attempting to dilute too much into a gallon or two of water will form a STRONG SOLUTION instead of a weak solution. It could heat up or boil as you mix it and could be very dangerous in many ways.
      Mix weak solutions as advised and live longer.

  5. I started using Calcium Hypochlorite and my berkey filter got clogged 5 times faster and had to spend $120 on new filters in just a few months. Was this a fluke or was it direct cause and effect?

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