How to Use Calcium Hypochlorite (Pool Shock) for Water Purification

When the water supply is compromised, the most common method of purifying contaminated water is boiling.  After all, if we're at home, we've got the pans and the stove to accomplish the task quickly.  And everyone knows how to boil water.

If the power is out, the next method for most people is adding bleach to the water and letting it stand.  Bleach is readily available at the grocery store and most people have it at home.

But liquid bleach is volatile, resulting in a pretty short shelf life, a serious disadvantage for long-term preparedness.  Clorox recommends only using bleach that is less than four months old for water purification purposes; the CDC and EPA both state that bleach up to six months old may be used.  (Clearly, Clorox is looking out for our best interests.)  Replacing bleach that frequently can become a bit of a challenge.  There are so many items we need to rotate and only so much money to go around.

Calcium hypochlorite to the rescue!

The usage of dry calcium hypochlorite powder (high-test granular calcium hypochlorite--HTH) to purify drinking water isn't some quack doomsday prepper notion of questionable efficacy.  Instructions for its usage are included in the Sanitary Control and Surveillance of Field Water Supplies publication issued by the military in 2010.  I tried to find a web address for just the information on using calcium hypochlorite but failed miserably.  All the links I unearthed were for the 200-page manual.  One of them is listed below.

When soldiers are out in the middle of nowhere and need to purify water, using powdered calcium hypochlorite is the preferred option.  Iodine, purification tablets, chlorine, and boiling are much further down on the list.

So what is calcium hypochlorite?  It is very closely related to sodium hypochlorite, common household bleach.  Unlike liquid bleach, however, powdered calcium hypochlorite is very stable, with about a ten-year shelf life when stored in a cool, dark place.  Because it is powdered, it takes very little space and stock solutions can be made on-demand instead of storing liquid bleach that deteriorates rather quickly.  With the quantities indicated in the table below, use the calcium hypochlorite powder you purchased to produce a 5% stock solution.

5% Calcium Hypochlorite Stock Solution
1 ½ cups water	1 teaspoon calcium hypochlorite powder
1 quart	2 ¾ teaspoons
2 quarts	5 ½ teaspoons
1 gallon	10 ¾ teaspoons

With the quantities indicated in the table below, use the 5% stock solution you created above to purify drinking water.

Amount of Stock Solution to Purify Water
Quantity of Water	Amount of HTH Solution for Clear Water	Amount of HTH Solution for Cloudy, Cold, or Questionable Water
1 quart	2 drops	4 drops
2 quarts	4 drops	8 drops
1 gallon	8 drops	16 drops
4 gallons	32 drops-1/2 teaspoon	3/4 teaspoon
5 gallons	1/2 teaspoon	1 teaspoon
6 gallons	2/3 teaspoon	1 1/3 teaspoons

Calcium hypochlorite powder may also be used directly to purify larger quantities of water.  For example, 1/8 teaspoon of the HTH powder may be stirred into a 55-gallon barrel with 50 gallons of water in it.  Cover and let stand for at least 24 hours.  

The Environmental Protection Agency suggests a different method on its website, as follows:

Add one heaping teaspoon (approximately ¼ ounce) of high-test granular calcium hypochlorite (HTH) to two gallons of water and stir until the particles have dissolved. The mixture will produce a chlorine solution of approximately 500 milligrams per liter. To disinfect water, add one part of the chlorine solution to each 100 parts of water you are treating. This is about the same as adding 1 pint (16 ounces) of the chlorine solution to 12.5 gallons of water. If the chlorine taste is too strong, pour the water from one clean container to another and let it stand for a few hours before use. 

So where exactly does one purchase this wonder chemical, and what exactly should be purchased?  Let me tell you, it can be pretty confusing.  Lots of times you'll see people saying to get pure calcium hypochlorite.  That's where most of the confusion comes from.  Accordingly to the afore-mentioned military publication, the strongest you can purchase is about 68-70%.   Because this is serious stuff, and because so much misinformation abounds on the internet, here is a direct quote from the Sanitary Control and Surveillance of Field Water Supplies publication:

"Calcium hypochlorite is a white granular or powdered chemical. When fresh, it typically contains 68 to 70 percent by weight available chlorine. It is commonly referred to as  HTH and is frequently used as a disinfectant in swimming pools."

However, most of what is currently available in stores and on Amazon is in the 68-73% range.  Due to my previous experience with bags disintegrating, I opted to buy calcium hypochlorite that comes in a plastic bottle.  And I thought it would be easier to use from a bottle that could be recapped.  It cost a few dollars more, but I think the extra expense was justified in this case.  And you don't need to buy a lot.  A single bag or bottle will treat over a thousand gallons of water.

As a hazardous chemical, calcium hypochlorite can chemically burn the eyes, skin, and mucous membranes. Wear gloves and safety glasses when using this product.

Storage: Calcium hypochlorite granules have a ten-year shelf life when stored in cool, dark conditions. It should be stored away from food. Off-gassing will make the plastic packaging brittle within a few years, after which time the bags will simply disintegrate with even the most careful handling. Even the plastic bucket we stored ours in cracked into pieces after about five years. You may wish to transfer the granules to a glass jar and tape the instructions and label to the outside.

This is the product I purchased on Amazon.  Like I said above, I paid more just to have a hard plastic bottle with a cap instead of a thin bag.

Links to related posts:
How to Purify Water with Bleach
Comparison of Water Treatment Methods
Basic Water Purification
SODIS Water Purification 

For further reading:
https://www.epa.gov/ground-water-and-drinking-water/emergency-disinfection-drinking-water
http://www.thepreparednesspodcast.com/wp-content/uploads/2012/08/Water-Disinfection.pdf
https://ia800505.us.archive.org/17/items/NAVMEDP501010SANITARYCONTROLANDSURVEILLANCEOFFIELDWATERSUPPLIES2010/NAVMED%20P-5010-10%20SANITARY%20CONTROL%20AND%20SURVEILLANCE%20OF%20FIELD%20WATER%20SUPPLIES%20%282010%29.pdf

 31 january 2021

12 march 2020