I bought some 55 gal drums that we are going to use for water storage.  I went through the exercise of doing a “shock chlorination” in order to sanitize the tanks and kill any bacteria that may have started growing in there.  I can imagine the only thing worse that not having any water during an emergency would be to find that the water you think you safely had  stashed away is now swimming with nasty bugs.

Here are the steps I used, which I think can easily be adjusted to any tank size you may have.

Step 1 – Mechanically Clean the Tank

Mechanically wash/rinse the tank.  I bought the tanks used, however, I was assured it never stored anything that was not safe when consumed.  So, for me this step was a quick rinse out of the barrel.  On a larger tank, this would involve using soap and brush to give a good cleaning.  If there was an easy way to get a brush down into the tanks I have, I would have done this too.

Rinsing the tank
Rinsing the tank

Step 2 – Determine the Amount of Bleach to Add

Determine the amount of bleach needed for 200 mg/l of chlorine.

I used a household bleach that was 6% chlorine.  6% = 0.06 = 60,000 ppm (same as mg/l).


Bleach containing 6% chlorine

Here is the equation to determine the amount of chlorine to add:


Plugging in the volume and concentrations the equation gives me the amount of bleach to add:

Notice, that I assume that the chlorine concentration of the water I’m adding is zero.  In reality there is a little bit in the City water that I’m using, but the concentration is so small it won’t make a big difference in the calculation.

Step 3 – “Bake” the Tank With Chlorine

So I’ve determined in the previous step that I need to add about 3 cups of the bleach. So, I filled the tank with water and added 3 cups of bleach to the 55 gal drum.  Remember, this isn’t for drinking, this is to kill the bacteria in the tank.

Measuring the bleach to add

I then let the tank sit or “bake” for 24 hours with this high concentration of chlorine.  This is important, because some bacteria require a certain amount of contact time for the chlorine to effectively break it down and kill it.

Step 4 – flush the tank out, and refill with fresh water

The title is self explanatory.  Empty the highly chlorinated water, and refill with clean water.

Now the tank should be effectively sanitized and ready for water storage.






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(2) Readers Comments

  1. Thanks for sharing this information. I am planning on purchasing some water drums and this is very helpful.

    • Glad this helped Pat!

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