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How to Use Pool Shock to Purify Water

Avatar for Jodie Weston Jodie Weston  |  Updated: October 20, 2020
How to Use Pool Shock to Purify Water

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If I were to ask how many of you store liquid bleach along with your other prepping supplies, I am certain that a good percentage of you would raise your hands.  Liquid bleach is a powerful disinfectant and sanitizer but did you know that there is something better?  Something with an almost indefinite shelf life that is inexpensive and takes almost no room to store?

That something is the chemical Calcium Hypochlorite most commonly known as Pool Shock.

How to Use Pool Shock to Purify Water - Backdoor Survival

I have known about Pool Shock for years but because it is not readily available in my area, I never took the time to search it out so I could stockpile some for my own emergency preps.  That has now changed and today I plan to show you how to use Pool Shock the easy way, step by step.

Why Not Bleach?

Before we start, you may be asking “why not use liquid chlorine bleach?”.  There are a few problems with liquid household bleach.  It takes a lot of room to store bleach plus the usable shelf life is only six months to a year depending on storage conditions.

The folks at Clorox say this:

The active ingredient in liquid bleach, sodium hypochlorite, is very sensitive to high heat and freezing, but under normal home storage conditions, it should still perform well for nine to twelve months.

In addition to limited shelf life, there is another problem. I have had reports from Backdoor Survival readers telling me that in their area, they can only purchase “Clorox Ultra” which is concentrated.  When I called Clorox to ask how to use concentrated bleach to purify water, they said that it was not intended to be used in that manner and why would I want to do that anyway.  Seriously, their representative actually said that.

Pool Shock – The Boilerplate

When I started doing research for this article, I visited some of the most respected survival and preparedness blogs and forums for background material.  After all, pool shock is pool shock and there must be some standards for use, right?

With just one exception, all of the sites I visited included this boilerplate from the EPA:

You can use granular calcium hypochlorite to disinfect water.

Add and dissolve one heaping teaspoon of high-test granular calcium hypochlorite (approximately ¼ ounce) for each two gallons of water, or 5 milliliters (approximately 7 grams) per 7.5 liters of water.

The mixture will produce a stock chlorine solution of approximately 500 milligrams per liter, since the calcium hypochlorite has available chlorine equal to 70 percent of its weight.

To disinfect water, add the chlorine solution in the ratio of one part of chlorine solution to each 100 parts of water to be treated. This is roughly equal to adding 1 pint (16 ounces) of stock chlorine to each 12.5 gallons of water or (approximately ½ liter to 50 liters of water) to be disinfected.

To remove any objectionable chlorine odor, aerate the disinfected water by pouring it back and forth from one clean container to another.

Have your eyes glazed over yet?  Mine have. Being an accountant, I like to deal in absolutes so what is this business about “one heaping teaspoon”?  Plus, what’s up with the references to “approximately” and “roughly”?

I decided that it was time to do my own testing, and sure enough, each time I measured out a heaping teaspoon, I had different results; they ran the gamut from 1 1/4 teaspoons to 2 teaspoons.  This made my head hurt.

Another thing.  Over and over I read that you should use pool shock that is a minimum of 78% calcium hypochlorite with the balance being inert ingredients.  Fair enough, but there are two problems with this. First, what you find locally maybe 68%, it may be 78%, or it may be something else.   Second, the EPA makes no such recommendation or at least none that I could find. They simply say “high-test”.

Did I mention this made my head hurt?

But there is more.  I actually found a couple of sites that said to use one heaping tablespoon of Pool Shock for every two gallons of water!  You know, just because you find something on the internet does not mean it is true.

My conclusion?  The exact amount and the exact percentage does not matter as long as it is within a reasonable range and close to the EPA standard.  I do think it is important that the pool shock does not contain other additives that may or may not be safe even when highly diluted.  Other than that, however, it is my belief that the precise percentage of Calcium Hypochlorite to inert ingredients does not matter as long as it is 68% or higher.

For my own use, I settled on 1 teaspoon of pool shock per gallon of water when making up my stock chlorine solution. Then, to disinfect water, I used 3/4 ounce of my pool shock solution to treat a gallon of water.  This makes it easy to calculate how much to use for water disinfection, regardless of the size of your container.

Step-by-Step: How to Purify Water Using Pool Shock

The first thing I did was to gather my supplies.  Notice that I used eye protection goggles and rubber gloves.  Other supplies included an empty bleach bottle, funnel, shot glass, and measuring spoons.

How to Use Pool Shock to Purify Water - Backdoor Survival

I verified the size of my stock chlorine solution container, namely a repurposed bleach bottle.  My bottle held 1.42 gallons and I wrote this on the outside with a Sharpie pen.  My intent, however, was to only prepare 1 gallon of stock solution to keep the math simple.

How to Use Pool Shock to Purify Water - Backdoor Survival

After donning my protection gear, I added water to my stock solution bottle, carefully measuring the quantity.  I used exactly one gallon of water.

How to Use Pool Shock to Purify Water - Backdoor Survival

I then measured out some pool shock; one level teaspoon to be exact.  I put the cap back on the bottle and swished it around a bit. I gave it a sniff test and it definitely smelled bleach-like.

How to Use Pool Shock to Purify Water - Backdoor Survival

The next step was to purify water.  I wanted to make drinking water and for me, the smaller the jug the better.  I chose a 64 ounce repurposed apple juice jug.  Remember the easy math?  The EPA says 1 part chlorine solution to 100 parts water so the math is 64/100 = .64 ounces.

Keeping things easy, that translates into approximately 2/3rd ounce.  Remember, the EPA guideline uses the word “approximately” all over the place.  That was good enough for me.  To easily measure the proper dilution, I used a mini shot glass that had measurement markings along the side.

How to Use Pool Shock to Purify Water - Backdoor Survival

Be sure to pour your pool shock into your water and not the other way around.  The last thing you want is to splash the solution on yourself on the surrounding surfaces (although you have probably noticed that I did this outdoors).

After preparing my newly purified drinking water, I drank up.  Three things.  I did not throw up, I did not get diarrhea and I did not get sick or die.

I am comfortable with the results even though the solution I made may have been slightly stronger than the EPA guidelines.  Then again, given the vagueness of the EPA guidelines, perhaps my measurements were spot on.

How to Use Pool Shock to Purify Water - Backdoor Survival

Note:  I did not find that my water had an objectionable smell or taste.  True, it was not sweet tasting like the water coming out of my Royal Berkey but it was palatable.  If your own purified water has an unpleasant odor, simply aerate it by pouring it back and forth between clean containers.  This trick applies to any water, not just water treated with pool shock.

How to Use Pool Shock to Purify Water - Backdoor Survival

Label your pool shock solution.  This is powerful stuff.  Get out your Sharpie and label the jug with as much information as you can.  Store it, in the same manner, you store liquid bleach, up high and away from pets and children and in a location that is cool, dark and dry.

Also, store your unused pool shock safely.  Because it is corrosive, I chose a mason jar with a plastic lid.  Plus, rather than empty the pool shock into the jar, I sealed the plastic bag it came in with a clip and stuffed the bag inside of the jar.

Other Handling and Storage Considerations

I contacted the manufacturer of the pool shock I purchased and requested a Material Safety Data Sheet on the product.  They promptly responded and here is what it said about handling and storage:

Keep product tightly sealed in original containers. Store product in a cool, dry, well-ventilated area. Store away from combustible or flammable products. Keep product packaging clean and free of all contamination, including, e.g. other pool treatment products, acids, organic materials, nitrogen-containing compounds, dry powder fire extinguishers (containing mono-ammonium phosphate), oxidizers, all corrosive liquids, flammable or combustible materials, etc.

Do not store product where the average daily temperature exceeds 95° F. Storage above this temperature may result in rapid decomposition, evolution of chlorine gas and heat sufficient to ignite combustible products.


Now that I have been through the process and understand the math, I am comfortable using pool shock to purify water for drinking, hygiene, and sanitation purposes.  It is not, however, an excuse for not storing water nor an excuse for not having a supply of traditional water purification liquids or tabs that are pre-measured and simple to carry with you in bug-out-bags and emergency kits.

As far as I am concerned, the pool shock I have purchased is reserved for dire emergency use, period.  Yes, I feel it is safe, but it is still a powerful chemical solution as is liquid bleach.  I will use it as the water purification method of last resort and if the time comes, I will be thankful I have it on hand.


I have to say this: I am not a chemist and I am not an expert.  My methods are my own and they work for me.  That being said, if you have any hesitation at all, visit other resources including the EPA and make the decision to use pool shock your own and not just something someone told you to do.  Here is a link:  Emergency Disinfection of Drinking Water.

The Final Word

Everywhere you look you will see a recommendation to store bleach for water purification. I have made that recommendation and so have many, if not most, of my blogging peers.  What you may not have seen is that liquid bleach has a limited shelf life of 6 to 12 months.  I fear that this could be leaving a lot of people ill-prepared to produce safe, potable water in an emergency.

This means that a person that began prepping a year ago, and does not know to rotate their bleach, is already living with false security when it comes to water purification.  And what about people that have been prepping longer?

As long as pool shock is stored properly, it will have an almost indefinite shelf life plus, a small one-pound package will treat many thousands of gallons of water. Ten thousand to be exact.  It can be mixed and used as potable water and as a disinfectant, just like bottled liquid bleach. So if you have a water storage tank and need something for emergency water disinfection, a hypochlorite solution could work out well for you.

At the end of the day, do your own research and decide for yourself.

Enjoy your next adventure through common sense and thoughtful preparation!

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88 Responses to “How to Use Pool Shock to Purify Water”

  1. Hi everyone. My husband and I are new to prepping. We bought 3.5 gal. “Water Bricks” to stock up on some water. We’ve been filling them with distilled water from the store. My questions are: 1. Do we have to rotate these once filled? (is there and expiration on them?) 2. Do we have to use a water purification form when we use them or as we fill them with the distilled water? Please help.

  2. 02Jan.2016

    If we experience an EMP attack, (Electronic Magnetic Pulse) where a Nuke is set off in the upper levels of the sky 10 to 20 miles up in the wild blue yonder, all the lights will go out and they will stay out for several years. The electronic in all the newer vehicles will be fried like in Sunny side Up is the way I like my eggs if you get my drift, if you don’t it means it won’t work ever again! All the electronics in the Auto Parts Stores will be fried too! The only thing that will run is a vehicle that uses the old points where you have to set the gap with a feeler gauge. Most people & a lot of the younger mechanics don’t know how to install or set the point gap in these older type vehicles, be they land or water type vehicles. Boats Air boats etc.
    Well thats all folks.

    I JUST PRAY The Rapture takes place first. I sure don’t want to have to deal with this type event. I am too old & crippled up to handle anything like that.

    Highly recommend you all, that is Hillbilly talk meaning all of you/everybody or every one get and read Ted Koppel’s book: Lights Out – Cyber Attack.

    Best Wishes to you all.

    MN1 Robert Briggs, USN Retired in Tennessee.

    The Best Thing any of us can do is call your Congressman/woman or Senator and DEMAND THEY START IMPEACHMENT PROCESS AGAINST THE idiot in the White House ASAP!
    MN1 Robert Briggs Vietnam Vet & 20 year USN Retiree.

    You can order it from Amazon, mine is due to arrive on 04Jan.2016.

    • I haven’t read ted Koppel’s book (Lights Out – Cyber Attack). I will put it on my list. I have read, One Second After by John Matherson. It is a novel but very thought provoking.

  3. Why not ten drops bleach: Clorox/Purex to one gal. of water from mountain stream,river or creek.

    Would this not purify it?

    Just wondering in TN.

    • The problem with bleach is that it has a limited shelf life of six months to a year. Undiluted pool shock will pretty much last forever plus a tiny bit goes a long way.

  4. Great article, as usual. One note for your, and everyones safety: chemicals should not be smelled in the way you pictured. Proper technique starts with wafting (using your hand to wave some of the smell toward your nose), if the smell is mild you may then move in for a stronger sniff. However, if you start by smelling as pictured, and the chemical is strong you can get hurt (or in some cases killed). Safety first.

  5. I am a licensed clinical laboratory scientist and just wanted to add a little info. One should not be entirely dependent on the EPA guidelines for solution strength. The solution strength needed to kill viruses and organisms is dependent on a number of factors. The cleanliness of how the water looks and smells before it is treated is probably the most important consideration. Of course drinking too much chlorine, is also unacceptable. Decontaminate the cleanest water available and be sure to first let it sit with good mixing for at least 20 minutes before drinking. Also, decontaminated water has a shelf life. I would not prepare more than a weeks worth at a time.

  6. When you ingest Calcium Hypochlorite (MMS2), it’s activated by stomach acid and produces hypochlorous acid which is a potent germ killer, normally found in the body. It does not release “chlorine” as some internet disinformation peddlers have falsely claimed. google,calcium hypochlorite mms 2

  7. They are “inert” ingredients that do not create a chemical reaction; mostly fillers. As far as the exact composition, in my own research I was told that they can vary from one brand to another but that they are harmless.

  8. Hi. Do you know what the other 32% is, that is not the Calcium Hypochlorite that is referred to on the label as “other ingredients”?

    • Not purifying contaminated water will kill you a lot faster than any damage lightly chlorinated water might do, and as others have pointed out just the act of pouring the water between two containers and aerating it will reduce the chlorine levels.

      Check out // for a truly frightening list of diseases found in untreated water supplies….

  9. Hi. Thank you for all of the great information, and I hope this doesn’t make your head hurt! I have probably visited 30-40 different websites regarding Calcium Hypochlorite (a mix of both government and personally maintained sites) and I would like to try and have something cleared up, because the information on this site, as well as the EPA’s own site is conflicting with most of the other sites.

    First, my purpose in analyzing Calcium Hypochlorite [Ca(ClO)2] is in its long-term stability as a water purifying agent. I try to be practical in my preparedness wherever possible, so for bugging out I want to base my water needs on the most common container in the world, the everyday 16.9 fl oz (500 mL) plastic water bottle. They are easy to carry, find and scavenge. Based on that, I ran some very quick calculations on high-test Calcium Hypochlorite (anything over 65% chlorine content, with the remainder being inert elements) and came up with the following…

    Using the commonly referenced guideline of 7 grams of Ca(ClO)2 per 2 gallons of water to create a 5-6% Chlorine Bleach Solution @ 500PPM, would mean that you only need 3.5 grams per gallon. There are 7.57 16.9 fl oz (500 mL) water bottles in a single gallon, so dividing 3.5 grams by 7.57 bottles yields .46 grams of Ca(ClO)2 to make a single 16.9 fl oz (500 mL) bottle of Chlorine Bleach Solution. I will just round this to 0.5 grams. My intent for my various go-bags (at home and in our cars) is to keep 2 small glass vials, each with .5 grams of pre-measured HTH Ca(ClO)2 in them, then each stored in sealed bags. They only take up about as much space as a pair of dice! That way if I am ever in a situation where I need to purify water or apply a disinfecting agent, it will be as simple as pouring the contents of one vial into a single water bottle. No thinking, no measuring required.

    Now for the confusing part. Just about every site out there (including the CDC, the WHO, FEMA,, and even the EPA) lists treating water based on the following…
    Using a stock of fresh 5-6% Hypochlorite Bleach @ 500PPM (or 500 mg/L), treating 1 Gallon of water:
    >> EPA (Normal Water) – 8 Drops [NOTE: this is a SIGNIFICANLTY different guideline than the 1:100 ratio that they use in their ‘general statement, see below]
    >> EPA (Questionable Water – Murky or Very Cold) – 16 Drops
    >> CDC Worst Case (Unknown Water, Unknown Bleach) – 40 Drops

    Several technical reports have even come out lately in Medical Journals that state even the 8 Drop guideline is too high (it should be closer to 4 or 5), that using 1PPM is all that is required over 45minutes to kill off any applicable foreign agents, everything else is just a waste. The studies were done in light of the weight associated with carrying bleach to remote African villages, so they were trying to be as precise as possible.

    I like using the 16 Drops / Gallon guideline, as this will help to account for the rapid deterioration of the bleach solution over the first 30 days (at which point it somewhat stabilizes), and the fact that I am using a clear water bottle instead of an opaque brown container, like the CDC recommends to inhibit deterioration. So, based on the 16 Drops, that would mean 2 Drops per 16.9 fl oz (500 mL) bottle of questionable water. “Drops” are certainly not a precise way to measure, but they are close enough, and can be defined as follows:
    >> 1 Teaspoon = 5 mL = 80 Drops [Google conversions lists it at 100 Drops]
    >> 1 fl oz = roughly 30 mL = 6 teaspoons = 480 Drops [Google conversions lists it at ~600 Drops]

    This article, and even the EPA guideline referenced at the very top of the article uses a 1:100 ratio for [chlorine solution] : [questionable water]. So, 1 Pint (or 16 fl oz) to 12.5 Gallons (or 1600 fl oz) to be exact, which is dead-on with the 1:100 ratio. Based on the fact that 1 Gallon contains 128 fl oz, that would mean you need to mix 1.28 fl oz of chlorine solution per gallon of water to be treated. This equates to approximately 38 mL, or nearly 8 teaspoons, or even 600 Drops as calculated above. If you use any of the online ‘drop conversion calculators’ online, it puts 1.28 fl oz in the 700-800 ballpark.

    So, to treat a gallon of water with a 5-6% Hypochlorite Bleach @ 500PPM, am I using 8-16 Drops, or 700-800 Drops? These guidelines are differing by nearly a factor of 100! If it were a factor of 2x or even 5x, I wouldn’t care, but these differences are significant. The person that I bought my 68% HTH Ca(ClO)2 actually provided guidelines imprinted on the sealed containers that use 5.5 grams per gallon to create a nearly 1,000 PPM solution and then states to use 1.5 fl oz of the stock chlorine to treat 1 gallon of water, which would result in a chlorine solution that is also significantly higher (almost double) to that of the EPA guidelines. And yes, the EPA completely contradicts itself by using the 1:100 ratio, and the 8 Drops per gallon, even on the same website. I have seen articles that say too high of a chlorine PPM will cause illness and diarrhea, but I have also seen articles that state this is entirely false, you won’t have any issues until you go to a much higher ratio, in fact it would be so unpalatable that you would recognize the high content right away.

    In summary, this is very confusing  but I will stick to the 16 Drops / Gallon guideline, for now. So, I will let the water settle and strain it first (if necessary), add 2-3 drops per 16.9 fl oz (500 mL) bottle of questionable water to be safe, let it sit for 30 min, then repeat if it doesn’t have a slight chlorine smell. If I were using the 1:100 guideline, I would be adding 80-100 drops or 5 mL (because a 16.9 fl oz is also precisely 500 mL), but that seems entirely wrong. Anyone with a kid that has used a 5 mL syringe dispenser for cough medicine knows how much 5 mL is, and that’s waaaaay too much to use to disinfect a single a single everyday plastic bottle of water. My conclusion is that the 1:100 ratio is simply wrong. Very wrong.

    Or, I must be missing something very simple, any feedback is greatly appreciated! Some of this has to do with the theory of small numbers when dealing with guidelines based on large numbers, but to be off by this much is concerning.


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